Pell vs. Tom I love the fishmen, and frankly, I think he has a lot of good buzz. Pell's success against Kuro was a fluke.
AoKiji vs. Franky Frankymania is at its peak right now, with the "he might be a nakama" rumours/stuff. Ao Kiji is an interesting character, but he's too small of a role to really engage hearts.
Robin vs. Nami (!!!!!!!!!!!!) Nami's made a lot of foes… she is often seen as greedy and whiney. My personal dislike for Robin won't do much.
Arlong vs. Ace Ace is full of potential, but Arlong's already delivered as a character.
Sanji vs. Smoker When the smoke clears (wait, it won't), strawhats are on home turf.
Crocodile vs. Hattori I still hold the grudge for Croc knocking my selection out in such complete massiveness, and I think Hattori gets a lot of votes as jokes. I think Croc's incredible cruelness plays both ways– some people really dislike him for it, some love him for it.
Bon Clay vs. Spandam An okama in drag versus a madman in bondage gear…. when did One Piece get so kinky? XD But seriously, I think BC has the name recognition and the "plays well with strawhats" favour.
Shanks vs. Chopper To me, it's another Ace v. Arlong. Shanks, we're just waiting and waiting for him to show the incredible potential we all know he has, but Chopper's been winning our hearts since Drum.
I guess I'll preemptively wave goodbye to Captain Smoker. Love the Moku-Moku, hate the rostering. :D