We all know the General 21 is how most EDH matches end. However, some cards (like Vengeful Archon) Prevent the next X damage you'd take. If a swing came in at you, with more than just an opposing general, could you choose to first negate that general's damage, and then worry about the other creatures? Or is all damage added up, so unless you negate the other damage first, you take the general's damage?
Sure. When you're being dealt damage by more creatures at the same time, and you can prevent only some of the damage, you choose which damage to prevent
(This can turn out handy when you don't want your opponent gaining life from a creature with lifelink, or when we're talking about General damage ;))
Quote from Comprehensive Rules »
615.7 If damage would be dealt to a player by two or more applicable sources at the same time, the player chooses which damage he prevents.
(This can turn out handy when you don't want your opponent gaining life from a creature with lifelink, or when we're talking about General damage ;))