I am using the bike primarily for the road, and to get some exercise and pleasure riding in. I am about 280 lbs. When I went to the LBS the first time I was on a 20" frame and I have very little clearance. When I rode the 17.5" frame the guy said that it looked pretty good once he adjusted the frame.
I had thought more recently about road bikes, but I have not looked to see if there are any in the $300 range.