Set Adrift is tempting, as we should be filling our yard with enough cheap spells to make the delve pretty effective. But we already have a good number of spells that temporarily remove a blocker, and I think blue is our splash so I'm a little hesitant to take another blue card. Taking another cheap prowess creature will fill out our deck nicely, so Jeskai Student is my pick.
The removal spells here are all too narrow or expensive for me to get excited about. Sultai Scavenger gets us an evasive warrior, which I am much more interested in.
1. Senate Guildmage: As you said, the mana efficiency of the abilities make this one pretty great. Both abilities provide value regardless of the game state. The loot is of course the premier ability, but the life gain can be pretty relevant depending on the match up. So, I agree that this one is the best, but it's not a slam dunk. Some of the other guildmage abilities can provide higher impact plays, but they tend to be more expensive/board dependent and therefore are not always "on".
2. Clan Guildmage: Both abilities are pretty good for a Gruul deck. Removing their biggest blocker is often enough to let you get in for those last points, and making a land into a 4/4 can provide a much needed threat or can play defense as a plan B. Both abilities are fairly mana efficient for what you get. The biggest drawbacks with this one is it doesn't really provide much value if you drop it early, and the abilities don't provide value if the opponent has gummed up the board enough.
3. House Guildmage: The Surveil ability gets big points due to Guild synergies. Being able to trigger a Dimir Spybug or Disinformation Campaign on command is really powerful. And of course the card selection is nice, but a fair bit more expensive than Senate's. Keeping a big threat tapped down can be a big deal too.
4. Legion Guildmage: Boros is the guild that cares most about this being a 2/2 for 2, but the abilities are no joke. The tapping ability will see the most use. It's a better, but more expensive version of Clan Guildmage's red ability basically. The 6 mana ability is sort of a plan B for when you're not able to beat them quickly. It's nice to have that late game inevitability for when the bigger decks are able to stabilize.
5. League Guildmage: Drawing a card is always nice, but four mana is a pretty big investment. The spell doubling ability can be powerful, but is also rather costly and dependent on having cheap spells to copy. This guildmage is middle of the pack due to how costly its abilities are, but the power level is high if you can get to the point where it starts going off.
6. Cult Guildmage: Like League, this has a four mana card advantage ability. Unlike League, your opponent can somewhat mitigate the card advantage by hand dumping or by keeping a land or two in hand. It can be quite strong in grindy matchups, though. The ping is an ability that can always be used and is quite cheap, but can often be somewhat low impact. It does synergize nicely with the Guild mechanic and provides some inevitability.
7. Swarm Guildmage: I don't have much experience with this one, but I'd say it's a bit sub par overall. This is the first guildmage on the list I would not be particularly excited to have in my deck. The green ability is a worse version of Senate's white ability. The menace ability is quite strong if you can set it up, but it's expensive and board dependent.
8. Syndicate Guildmage: Again we have a cheaper, but weaker version of Legion's white ability. This time, though, the ability is actually useless on certain boards. The second ability is basically a worse version of Legion's other ability. It does cost one mana less, but at the point at which you're starting to dome them the extra point of damage is more likely to matter. Syndicate can be quite powerful, but it also has a decent chance of being completely useless, so it gets a pretty low spot overall.
9. Combine Guildmage: I was pretty disappointed with this card when I tried it out. Tacking on two extra mana to a creature is a big investment, and an extra +1/+1 counter just often isn't worth it. It also is a bit of a nonbo with Adapt. Moving the counters around can be nice to make combat difficult for the opponent, but overall this one just feels a bit low impact.
10. Conclave Guildmage: How the mighty have fallen. Selesnya typically gets one of the best Guildmages, but this time around we have two pretty unexciting abilities. The green ability is cheap, but often doesn't do anything. Producing 2/2's is a nice ability, but it comes at such a steep price that it often just won't do much by the time you are able to activate it.
Tough pick. Throttle is tempting given how few removal tools we have, but the fact that we just picked up another red bomb pushes us toward wanting better fixing. I think if the removal tool was better I'd go for it, but Throttle is expensive AND conditional, so I'm going to pass in favor of one of the lands. I think Wind-Scarred Crag is the best of those. It's better than Bloodfell Caves because taking Crag screws over our Jeskai opponents. And it's better than Scoured Barrens because Crag replaces a Mountain, which means we have one less land in our deck that can't cast Chiefs on turn two.
The cards I'm looking at here are Snowhorn Rider, Glacial Stalker, and Monastery Flock. I think we need win cons more than early defense right now, so the Flock is out. I think our mana base is going to be rough enough that taking the more consistent, but slightly less powerful fatty is the better choice. So, Glacial Stalker it is.
Wingmate Roc. This is a little awkward given the double white, and will probably necessitate playing one or two Abzan Banners. But I'm not passing up a pick 3 Roc.
This pack is insane for us! Four great morphs and two lands in our colors, plus a few other cards in our colors. I don't think we can pass on the crazy two for one potential that Kheru Spellsnatcher offers. This deck is perfect for that effect, since we should have no problem leaving up mana, and if the opponent doesn't cast anything worth countering we can just flip something else up or throw down a Pearl Lake Ancient.
Dazzling Ramparts. This pick looks weird, but hear me out. On the surface it looks like I'm taking an inferior white card here, but contextually it makes sense. We're splashing white, so Bond-Kin will rarely come down turn 2. So we usually can't trade it off early, nor will we have the benefit of building it up over the course of the game with our spare mana. It's also a bad late top-deck, as it's just a measly 2/1 that can't block well. If we're casting a white spell on turn 5 or 6 or whatever after we draw into our white mana, we want it to be impactful the turn it comes down. The wall can block basically any ground creature without dying, and the turn after it comes down it can stop fliers too. Control decks like these types of cards that can hold off a threat without expending a removal spell. I think it's the better fit.
Jungle Hollow is tempting for me, but given that Anafenza is the only card we need green to cast, and that we are somewhat lacking in playables, I'm going to give it a pass. As far as the two drops go, I'm not really sold on the Chief. Scale is worse than Edge, and we didn't really get there on warriors anyway. Discounting Zurgo who will probably get cut, and who doesn't really benefit much from Scale, we have six warriors. That includes Unyielding Krumar and Kin-Tree Warden, both of which I would ideally like to cut. Ainok Bond-Kin is easier to cast, and becomes a late game powerhouse, which is a rare feat for a two drop.
Hordemate needs too much to go right to be a good card, and I'm certainly not taking it over a fixing land. Swiftwater Cliffs over Bivouac for me. We're basically 0% to ever splash a green card, and the life gain can be relevant. Picking up our fourth piece of fixing here gives us more flexibility to pick up stronger cards going forward.
2. Clan Guildmage: Both abilities are pretty good for a Gruul deck. Removing their biggest blocker is often enough to let you get in for those last points, and making a land into a 4/4 can provide a much needed threat or can play defense as a plan B. Both abilities are fairly mana efficient for what you get. The biggest drawbacks with this one is it doesn't really provide much value if you drop it early, and the abilities don't provide value if the opponent has gummed up the board enough.
3. House Guildmage: The Surveil ability gets big points due to Guild synergies. Being able to trigger a Dimir Spybug or Disinformation Campaign on command is really powerful. And of course the card selection is nice, but a fair bit more expensive than Senate's. Keeping a big threat tapped down can be a big deal too.
4. Legion Guildmage: Boros is the guild that cares most about this being a 2/2 for 2, but the abilities are no joke. The tapping ability will see the most use. It's a better, but more expensive version of Clan Guildmage's red ability basically. The 6 mana ability is sort of a plan B for when you're not able to beat them quickly. It's nice to have that late game inevitability for when the bigger decks are able to stabilize.
5. League Guildmage: Drawing a card is always nice, but four mana is a pretty big investment. The spell doubling ability can be powerful, but is also rather costly and dependent on having cheap spells to copy. This guildmage is middle of the pack due to how costly its abilities are, but the power level is high if you can get to the point where it starts going off.
6. Cult Guildmage: Like League, this has a four mana card advantage ability. Unlike League, your opponent can somewhat mitigate the card advantage by hand dumping or by keeping a land or two in hand. It can be quite strong in grindy matchups, though. The ping is an ability that can always be used and is quite cheap, but can often be somewhat low impact. It does synergize nicely with the Guild mechanic and provides some inevitability.
7. Swarm Guildmage: I don't have much experience with this one, but I'd say it's a bit sub par overall. This is the first guildmage on the list I would not be particularly excited to have in my deck. The green ability is a worse version of Senate's white ability. The menace ability is quite strong if you can set it up, but it's expensive and board dependent.
8. Syndicate Guildmage: Again we have a cheaper, but weaker version of Legion's white ability. This time, though, the ability is actually useless on certain boards. The second ability is basically a worse version of Legion's other ability. It does cost one mana less, but at the point at which you're starting to dome them the extra point of damage is more likely to matter. Syndicate can be quite powerful, but it also has a decent chance of being completely useless, so it gets a pretty low spot overall.
9. Combine Guildmage: I was pretty disappointed with this card when I tried it out. Tacking on two extra mana to a creature is a big investment, and an extra +1/+1 counter just often isn't worth it. It also is a bit of a nonbo with Adapt. Moving the counters around can be nice to make combat difficult for the opponent, but overall this one just feels a bit low impact.
10. Conclave Guildmage: How the mighty have fallen. Selesnya typically gets one of the best Guildmages, but this time around we have two pretty unexciting abilities. The green ability is cheap, but often doesn't do anything. Producing 2/2's is a nice ability, but it comes at such a steep price that it often just won't do much by the time you are able to activate it.