I chose Ace Trainer, but I'm kind of a mix. When going through the game I usually just use decent pokemon I like the look of (since the storyline game is generally easy enough that I don't need much else) but if I start on some of the side stuff or battling with my friends, I normally make a very well built team, but I'm no where near Pokemaniac status. Worse than some but better than most.
On top of that, I tend to think of stuff I would like to see done, or what team I would like to have in reality, etc, etc. So Ace trainer seemed to be the way to go.