1. Pinkie - Well, duh. She's the element of laughter, and the one pony who can always make me laugh
2. Twilight - She can be really funny at times (Especially in Lesson Zero and It's About Time) even if she's not always trying to be funny.
3. Rarity - She doesn't necessarily make me laugh, but it still makes me smile when she gets hit in the head with a rock. (The revenge of Tom!)
4. Fluttershy - She isn't really the kind of pony to make someone laugh. She's the most adorable pony in the world (in my opinion), but it doesn't make her that funny really.
5. Tie between Rainbow and Applejack - Well, neither of them are really funny to me...