I see Bush as more of a Dante Hall type of guy, who can change the momentum of a game simply through a few touches.
Peterson is a feature back, wear down the defense, control the clock, and then break a big run every once and a while.
They're really different players and tough to compare. Realistically, Bush isn't a running back. He really doesn't have a position. He's a playmaker, but he doesn't really fit into an every-down sort of situation.
Peterson, though young, is a prototypical running back. He's not there yet, but he has the potential to be a really special back.
Personally, I'd take the feature back, but Bush is certainly talented and very important to his team.