I think it's gonna be chopper with his massive points

Hard to say since they've yet to properly display their latest powers...

Brooke has led a "rock star" life, so I can't imagine he'd have much time to improve his fighting abilities, though he might have new skills.

Chopper seems to have focused on a more scholarly training, but had more time to train himself physically than Brooke. With those combined, he's surely more powerful, though just how powerful is too ambiguous at the moment for me to decide.

Nami seems to have focused on studying as well, but her fighting style relies on her intelligence and ingenuity, plus her weapons got an upgrade, so she probably improved more than Chopper and Brooke over the two years. However, her power is very specialized, so it's hard to figure where she stands overall.

I vote for Usopp as strongest. During the two years, he survived on that dangerous island, improving his physique, his ingenuity, and his supply of creative ammo for sniping. He was originally like Nami, specialized (in sniping), but he could probably hold his own in combat as well now (as long as the enemy isn't too strong).

@OP: know that each series has it's own forum. If you're discussing specific titles please use them.

Moved to One piece forum.