Theys, alot of bikes in the $800 range. I can tell you that the Rockhopper comp is a great bike, I have one. I bought an 08 this year, and found a nice deal. I'm no fan of the 09 mainly because of the sram componets, and dart 3 fork.
I'd test ride as many as possible, pic 3 that fit realy well. Then see how they stack up componet wise, and price of course. Look for a nice shock with a lock-out, and rebound adjustment. Quality shifters are the next thing I'de look at. The rest is a simple upgrade later on, or when something breaks. Personaly, I like shimano over SRAM...But sram make some decent high end parts.
If you don't know how to wrench a bike, you'll have to find a GOOD bike shop. Go over and talk to the mechanics. The sales guys somtimes don't know jack. I'de learn all I could about bikes before I spent my "bird" money.