Crazy Eyes since she's so diverse. Funny, crazy, honest and once in a while very deep and thoughtful. I also love the tragic side of her character. She never wanted to harm anyone but her nature just doesn't allow her to live a normal life even though she tries to be a good person.
Almost all of them lol
I still defiantly love Piper even though most people hated her last season lol. But Gloria, Poussey and Crazy Eyes are my favs, but every character is morally gray enough for me not to be able to categorize firmly into like and dislike
Chang 
, I hope we get a backstory of hers next szn 
One of the funniest characters with an interesting and sad backstory.