I think my favorite intern is Fisher, and I don't know why. I really can't give an explanation, other than every time Fisher is in the episode, I perk up. I think that dark humor is missing in the show, and I enjoy it. (Did anyone see the episode where they go see Avatar?
Then, next would be Clark. To me, he's an intern version of Brennan. How she would have been before she met Booth, and he 'humanized' her. Strictly business, and I mean come on. He found something on a bone that Zack missed. He's brilliant. There's also the clear tension between him and Angela, not in the way she and Hodgins have it, but it's there. She makes him uncomfortable, and though he tries to hide it, it allows for a bit of Clark to get into the workplace.
I dislike Daisy as an intern, though she is pretty great for Sweets. Haha.