I actually have to say Cole. Because really in Advent Children Barret didn't seem as mobile as I'd thought he would be. Plus he can only use the Big Shot once and has to wait to fire or anything for his gun arm to recharge.
Cole on the other hand was a thrashball player (I'm guessing that game is like Football just more thrashing or something) and is an experience soldier for COG. I have to give this fight to the Cole Train.