Male:
1. Luffy - as the series goes on he looks more mature and pretty darn sexy, not to mention that his serious face rodsftjgdf. 
2. Usopp - the fact that he manages to look so hot with that nose makes him even more awesome.
3. Franky when he was 20. Ee. 
4. Iceberg when he was younger
5. Kaku! He's too cute.
Female:
1. Nami and Robin - they're both beautiful in their own way, how can I choose?! Ah, I feel like Sanji sometimes.
2. Vivi - Too pretty. And best hair in history of anime after Anthy from SKU.
3. Calipha. Mmm, she could sexually harass me anytime. As long as I come out alive from it.
4. Alvida - after her transformating, obviously.
5. Bellemere, I guess. She never really striked me as a wonderful beauty [must be the hair], but she's still darn sexy and AWESOME. 
Other[? o.o]:
1. Robin's turtle
2. Robin's pig [from the "Excuse me baby, no parking on the battle grounds" image]
3. Chopper
4. Carue
5. Pierre FTW