What size to get?
 

I am looking at a Trek 7300 and the 20-inch seems to be good, though the next size up was also good. When sitting on the seat, my feet touch the ground when on the 20-inch though not on the next size up. Which way is better?

Thanks.

While pedaling, your legs should be almost fully extended at the bottom of the stroke. If your feet touch the ground while seated, the saddle is much too low. The frame may or may not be too small. Saddle height is largely independent of frame size.

When I bought my 7.3 FX I opted for the next size up, 22.5" vs 20". The LBS swapped on a shorter stem and moved the seat around a bit. It felt much better than the 20" in my opinion and is very comfortable on long rides. According to trek I should be on the 20" since I am 5'10" but I guess everyone is different.