The hardrock is way to go. It is a super burly frame which is good a 255lbs rider and they are highly versital. If you do decide to go with any of the hardrocks look into upgrading the fork because you are such a big guy. Other than that the hardrock is perfect.
Temeraroius suggested the rockhopper but i disagree. The rockhopper is a lighter frame and many people think therefor it is better, but because you are such a big guy go with the hardrock because it the frame is stronger.