Couple questions:
Are you going to be mainly road riding or bombing trails? You can't go wrong with Kona, Trek, or Gary Fisher. All three make great stuff. I don't know much about GT, so can't say anything good/bad about them.
PS: You might shop around the stores in your area. One shop may have a Kona for one price, another shop may have a significant price cut on the same thing. I picked up my commute bike (a Kona Lana'i) for a great price from a LBS while another LBS wouldn't cut any slack on the price. To boot, the store that had a good price tossed in a free
http://tinyurl.com/ndf4g which is being used to keep the bike from being stolen out of my courtyard.