Among the Strawhats I like Chopper and Sanji best (he's a gentleman/nice to women).
4Kids ruined this anime for me.
Try the Shaboady Archipelago (with the 11 supernovas) and Whitebeard War arcs. They are probably the best ones in the series. My brother also liked them best.
I know this is an old thread, but I don't care.
For me it's Robin. I really like villains who become allies, but even aside from that, her arc is one of the best in the series.