Whatever you do, don't think that you should get a hybrid. When I first started out I was in the same boat as you, didn't think I would be doing much mountain biking. Figured with the lack of trails I have around me I would be riding more dirt trails and roads. Once I got on a actual trail I loved it and was pissed my bike couldn't handle some of the terrain I was riding.
If I were you and you do want to use your bike for roads and mountain biking get a hardtail. I bought a Specialized Rockhopper and love it. Wheel size is up to you as well, I liked 29er because you can ride over alot of stuff easily with bigger wheels.
Since you are looking for a bike to use on the road as well as trails make sure you get something with a lockout fork. That way you won't be absorbing all your energy in the front fork. That is also why I would recommend against a full suspension bike. When you are riding on the streets it will absorb alot of your force and make riding on flat ground harder.
This is the one I got,
http://www.specialized.com/us/en/bikes/mountain/rockhopper/rockhopper-comp-29
Worked out a deal and paid just under $1000 for it. But from a local shop, test a few bikes and just see what feels the most comfortable to you.