Seeing as I dont care about slight framerate differences or tiny differences in graphics, that does not really matter, but obviously if it is major, that would lead me towards the better one
However, I have not really had to make that choice yet, though I think that achievements will lead me to getting more Xbox games, and indeed I chose to get AC, on sale, for Xbox 360 because of the achievements (though I have noticed that it seems to have more technical issues on 360 than when I played it through on PS3.
I think trophies will be less important than acheivements for me until they are more widespread, but for now, they are the major turning point.
Other than that, the other main consideration in multiplayer, and any with MP that I will play online I will get on PS3, because I have no interest in paying for Live
Stuff like the controlers do not make much difference, but I am sure once trophies are more widespread I will have to look at stuff like that
EDIT: forgot about extra content, but the rumours of Kratos on the PS3 SC IV are making me get that version, even though they have been shown to be false. As for others, unless it is something major it wont be a more important than achievements
