i'm a MTBer at heart... riding some nice flowing singletrack is prob the best place in the world for me... but the last time I hit the trail I was so out of shape I didn't bother going back... it took me over a week to recuperate... that was largely my fault... mid summer in TX, even drinking plenty I managed to get dehydrated... I ended up turning the bike into something more road oriented... and then selling the frame and swapping the parts onto a touring bike... I wanted something that was decent on the road, that I could putz along on greenways and that sort of things... in the back of my mind I also loved the idea of touring so I went with a surly disc trucker (allowed me to use my MTB parts with minimal parts swapping)... it is a great bike for solo rides on poor roads but a few months later I built up a road bike... if it wasn't for me wanting to tour (have a nice 450 mile loaded tour coming up soon I think a CX bike would have been the best compromise for me... a change of tires and possible raise the stem a bit for hitting mild trails yet near the speed and comfort/hand positions of a road bike while on the road

for MTB... I like giant... they make good solid MTBs... but in your price range the forks are pretty crap especially for bigger clyds like us... if you really want to hit REAL MTB trails go with a MTB... but get a better fork or a rigid fork... large volume front tire run at lower pressure and learning to navigate the trail rigid will make yo a better rider when/if you add suspension down the road.

but be realistic with yourself... if real trail riding isn't in your future i'd seriously consider a CX bike... while it is a compromise it's not as large of a compromise as the MTB