Charlie-III
I wanna be Dave
Stock, they're the same in operation.
Hacked, they are the same in operation.
OverkillRC sells hack kits for either one if you want to do it yourself. One advantage of doing your own hack is that you can do firmware updates down the road as they come up.
The GT3C looks a little better, feels a little better in my hand.
The GT3B is a little cheaper new, the GT3C can be found in a few different colors on Ebay (you have to look around, they "come & go" at times) but this raises the price a little more if you want a different color.