Hunter.
Double jump is a lot faster than the rest and it actually has a lot more maneuverability since you can jump once in one direction, then double jump in another and it's all very fast. I found myself scraping walls trying to get to a higher vantage point with the Warlock and Titan a lot, but not with the Hunter. The Warlock's jump ability in particular was just really bad IMO. You're kind of just hovering there without much speed meaning you're a hovering duck, atleast the Titan moves kind of fast.
The special isn't as good since there's more work on the player (you actually have to aim), but I still liked it. It was a lot more consistent than the rest, especially compared to the Titan's which is a great AOE attack and can take out a bunch of things at once but you're never (well, I was never) really sure how far the character is gonna dash to smash.
I dislike the throwing knife though, since you can accidentally press it and put it into cooldown. The other classes' special melees don't go into cooldown when you don't hit anything.
Overall, they're all pretty much the same. I guess they'll change more as you progress but it was pretty disappointing. I was sort of expecting classes more like those in Borderlands, but I suppose the PVP won't be very balanced that way.