Law. His backstory, like Robin's really moved me and it's my favorite so far. He's got an intriguing personality that reminds me of my own at times, and he's just fun to see. His development and relationship with Corazon really cemented his status as my favorite character.
Zoro - Badass
Kizaru - Troll master, and he is also my favorite marine (often underrated, too)
Luffy - I am suppose to like him
Robin - I like the charm she gives off, especially while around Chopper.
Too many to choose from but Luffy for sure then Smoker...his tenacity and commitment while still remaining a good marine and person is what draws me to him.
My favorite is Nico Robin. She is smart, beautiful, mature, and has one hell of an incredibly amazing devil fruit, not to mention that her backstory was the only SH backstory that almost made me cry.
My second favorite would be Rob Lucci simply because of badass he is, especially with him being a master of Rokushiki, my favorite fighting style in the series so far.