There are so many options for frame material nowadays, not to mention suspension designs and the combination of the two.
Why do you want to avoid full suspension? Weight isn't much of an issue anymore with the new generation of lightweight full suspension bikes! Ride quality? Can only be improved with full suspension. You can ride longer with less fatigue and can ride faster through rough terrain! Maintainence? O.k. I'll give you that one! There is a little more involved but not enough to forego the other benefits! Looks? That's personal, but I think full suspn looks great!
O.k. enough rambling! Frame material choice depends on the type of riding you are planning on doing, and the ride quality you prefer. As a newbie to the mountain biking community, I'd save your money and stick with aluminum until you get more experience as to what you like! I'd spend more on better components and then upgrade your frame in a few years!
As a review of my (limited) knowledge on the subject;
Steel: Smooth Ride, easy to work with, can be heavy, repairable!
Aluminum: Stiffer ride, easy to manipulate, lighter weight, limited life span if abused, lower cost
Carbon Fiber: High Strength to weight ratio, thus lighter frame, flexible (good or bad depending on where the flex is), once damaged it's trash, non-corrosive
Titanium: High Modulus of elasticity so very smooth ride, costly to manipulate and properly weld, beautiful natural finish, will last forvever!
If you're planning on racing, then carbon or titanium will provide very light bikes. If you're going to do all around riding they don't take abuse well, and are very costly to repair! Many companies that do aluminum frames well, such as Cannondale have been able to manipulate the tubes to cut weight and provide favorable ride characterists that make it a great choice! Suspension frames are mainly aluminum due to the ability to manipulate this material. There are also frames utilizing carbon in the seat stays to provide flex in the frame to give a smoother ride!
There are just soooooo many option available to you for $2,000.00. I suggest getting a decent aluminum frame with XT or XTR components and a good fork and riding the heck out of the thing. Try riding your buddies bikes and find out what you like in a frame. I've been riding for over 10 years and I still don't know!
Good Luck
L8R
