Either red or orange. Blue's a bit too blocky, like a monospaced font -- nothing wrong with it, but it visually clashes against the wavy/curvy speech bubble you're using here.
Green's not terrible, but it's one I'd save for special ocassions/characters. It's too dramatic for normal, everyday talk (but if you're going with an over-the-top kind of humor, it could work).
The odd capitalization in orange's font, while not bad-looking (it reminds me of the font Netherrealm will use for the upcoming Mortal Kombat X), looks a bit awkward as-is. Maybe you could rearrange and reshape your speech bubbles to take a proper advantage of its unique look.
Red's the safer choice here. It's easily legible and the caligraphy touches look nice with the type of bubbles you're using.
Hope this helps!