I started out years ago as strictly a mountain biker and slowly evolved into riding both road and MTB. I did that as a matter of concenience because where I lived in Va we used to have to drive 1.5 hours each way to Williamsburg to get to any appreciable trails. Since I've moved to PA and now have over 100 miles of singletrack within 30 minutes of my house I mostly mountain bike because I've always preferred singletrack MTB over road riding. I've had more mountain bikes than I can count and had a full stable of mountain bikes when I moved to PA but had a firesale and reduced it down to the one bike I found myself choosing over the rest all the time. I personally prefer full suspension over hardtails but I agree with cycco's post above, front suspension gives you more control in rough terrain over a rigid so I would at a minimum get at least a front suspension bike.
Here's a pic of my bike I took at a trail head during a recent trip to Richmond. It's an old 97 Ellsworth Truth with M950 XTR.
