brittonal said:
Would anyone else like to share information with the new guy? Maybe reasons?
Okay, I'll add my two cents, but understand that my experience is 10 years old and the reason I'm browsing this forum is I am looking for a new bike myself and have been out of the scene for a while.
$800 kind of limits your selections to a new, lower-end hardtail or the used market. Nothing wrong with used, but since my mechanical skills are limited to cleaning and adjusting the drive train and shifters, I am looking at a new bike with a warranty from a LBS (local bike shop). Nothing wrong with a hardtail either, but I prefer a full-suspension bike because it allows me to feel more confident on descents. I don't do big drops, but suspension on both ends soaks up the bumps better than my arms and legs can, so the wheels stay "hooked up" longer. That gives me better control, especially under braking. But hardtails are lighter at the same price point, and mechanically simpler, so they're easier to maintain, too.
The other poster recommended a Specialized
Rockhopper. That line has been around forever (I actually have a '92 Rockhopper Comp that I converted to a commuter/beater bike and still gets ridden regularly). The new bike has a basic suspension fork with lockout, so you can ride it like a rigid bike on the street and on climbs without getting "pedal bob," which robs you of pedaling efficiency and feels like walking on a trampoline. You also get mechanical disc brakes. Top bikes get hydraulic disc brakes, so I'm going to assume they're better

I'm sure they're comparable to good rim brakes, so they'll probably stop you when you need them. The difference is probably how they feel, which is important when you're trying to control brake pressure to maintain traction while slowing.
Everything else about the bike is pretty basic -- for $800, you're not going to get anything exotic -- but if you're a new rider, it's not a bad idea to just get something that fits and get out on the trails.
Speaking of fit, this is very important. If you're really a newbie, the only real dimension that matters is the seat-to-pedal distance. Get that wrong and you could cause some knee pain. Everything else, you'll learn what seat-to-bar distance and bar height you like from trial and error. This is one reason to buy from a LBS. They'll have the same bike in several sizes, so you can get a good fit. You can also try different brands/models in your price range and compare them side-by-side. Even if the seat-to-pedal distance is the same on different bikes, their frame geometry will make them feel different. If you're going the used route, bring a knowledgeable friend who can make sure your seat-to-pedal distance is in the ballpark.
HTH,
MTB