i play a Martin D 16 RGT. this basically means a dreadnought size guitar with rosewood back and sides and a spruce top. This is a pretty large guitar, and as a result the sound has a lot of depth. The rosewood produces a much warmer sound then mahogony. My buddy has a DM, which is mahogony and I play it quite a bit. I do like mine more though. It is better IMO if you are playing by yourself, but the mahogony tends to project more when playing with others. I would recommend you go to a good music store and they will hopefully sit you down and just start handing you all sorts of guitars based on your wants and needs and you just play until you come up with the right one. I have no bias towards Martin, I just think its a classic US company that consistently produces fine products that last. Despite the fact that my martin was a lot of money, it is a purchase that will last my life time. And it sounds better and plays better the more you play it. I cant wait to play that guitar when its 30 years old. If i were you I would also look into Taylor, Gibson (these are actually made where I live here in Bozeman, MT,) maybe Guild (i believe this is Fenders acoustic line) and Collings (if you have a lot of money to spend.) Collings are supposedly great guitars, but I have yet to play one. They are in the several thousand dollar price range. Check out www.elderly.com.
This is my local music shop where I grew up in Michigan. They are one of the best guitar shops in the country imo. I hope this helps!