Power programmer questions

I've got a 2003 Silverado with the 5.3 V-8. I'm looking to get more power (have the K&N intake on the way) and am thinking about getting a power programmer. Which one is better the hypertech or the granatelli? Also will these void the factory warranty? Any help would be greatly appreciated.

I didn't realize that Superchips also makes one so I guess throw that one into the mix to. Anybody who has any info on the three or could recommend one to me?

I have the Hypertech on mine, I have had it for 40K miles and have had absoultely no problems with it. I have un-installed it to take the truck back to the dealer, and can't hardly stand to drive it w/it un-installed. The only thing that you mudt do that I didnt particularly like is switching to 93 octane gas, but to get full performance, I think you must do this with all of them.