I am going to college soon and need a new bike that will last. It will be driven on mostly pavement, but also some dirt/gravel trails from time to time, so I was leaning toward a mountain bike that is good on the road or a hybrid bike. So far I was looking at the Giant Sedona and Boulder, the Specialized Rockhopper and Crosstrail/Crosstrail Sport and The Trek 7.2FX. I am afraid that some of the hybrids might be a bit too roady to use on rough dirt or gravel trails but that the mountain bikes might cause back strain after extended periods and require more effort because of the different wheel size and gearing. Any thoughts or other suggestions? I havent ridden any of them yet, but I will before buying.