+1 on rim choice being far more important.
Purely from reading and hearing what extremely experienced mechanics have said, I agree with the argument that double butted spokes are superior. In fact, I've yet to hear of a substantial argument that supports straight gauge spokes.
That being said, I ride straight gauge on my touring bike and have yet to break a spoke. However, when a spoke breaks, it's usually at the head, and the head diameter is exactly the same on straight gauge and double butted spokes(well, the ones we're talking about). I think a spoke breaking on a wheel is a symptom of a bigger problem, like an improperly built wheel, or worn out parts.
I think the only benefit of straight gauge spokes is if something were to get caught in your wheel like a branch or something, and actually stress the middle of the spoke by bending or twisting it.
Eh, I'm not saying anything that hasn't already been said. Another vote for butted, although not through experience.