Of the list you have, two look better than the rest - the Giant XTC 2 and the Specialized Rockhopper comp disc. The Giant has a really good frame, easily worth upgrades later on. The Specialized has 20mm more travel than the Giant, so its down to you there. Personally i would go with the Specialized as although its a bit heavier, it has a slightly stronger frame, and with the longer travel fork, will take a bit more of a hammering. If you are looking for solely trail speed, then go for the Giant, but if you want the ability to ride a bit harder and maybe a bit more aggresively, go for the Specialized.

good luck with your choice!