ive heard good things about alot of tuners, I would say it depends on what your wanting to do with the truck. If your just looking for a few extra ponies for fun id get an Edge, or maybe a BullyDog or somthing like that.
If your looking to tune the truck for compitition (drags, sled pulling, big ponies!) and really want to get into customizing all the different parameters of performance, i would get an SCT.
Ive got an Xcal3 and love it. Theres dozens of different vendors who can build custom tunes for it. Only downside I see with the SCT is theres no "shift on the fly" between tunes. Good luck!