I haven't bicycled in more than a decade. I am considering getting back into bicycling for commute/fitness.

I went to Trek San Jose to try out some of their bicycles. I tried the 7.3fx. The LBS person recommended the 22.5in frame based on my height, etc. I tried that and the 20in frame.

I tried two seat positions. One where my feet could easily touch the ground when I was on the saddle. The second where only my toes touched the ground when I was on the saddle. Overall, the second seat position was uncomfortable for me -- I'd much rather be able to put my feet on the ground until I'm more experienced.

I couldn't quite tell much of a difference between the two frame sizes. 20in seemed more comfortable in the first seat position. 22.5in seemed a little bit more balanced in the second seat position. But, as I was comparison riding the two bicycles, I found myself becoming more comfortable, so I am not sure if my comparison is really that objective.

In both frame sizes, there was enough clearance between me and the top bar.

How do I decide which is better? I want to ensure that I don't make a decision based on current comfort that I will regret in the future.

Thanks.