Go with the rigid bike. In this price range, front suspension and full suspension are really heavy and don't work particularly well. You'll probably knock 8 or 10 pounds off the bike weight between the full suspension and the rigid. Why does this matter? It makes the bike respond quickly, handle better, and just flat be more of a pleasure to zip around on. Ride it as-is, when the tires wear out, put on some slick or semi-slick tires. It will really liven up the bike. This will make a perfectly good "commuter" for you. Enjoy it - it's free.
Spend your money on a good seat. Gel seats "seem" like a good idea, but they are usually just squishy-ness over a crappy seat. A bike shop will carry good seats. Get one that fits your bones - a little padding is fine, but the base seat must fit YOU because no amount of gel/padding/pillows will ever make up for the poor fit.
As far as the comments regarding full suspension being a handicap on a climb - I don't necessarily agree. On an entry level bikes - agreed - the weight and efficiency are unacceptable. On high end equipment the weight difference is not so much, pedaling efficiency is very good, and most will have a "lock out" on the shock. Flip the lever and it's a hard tail for a climb.
This is my full suspension bike. This is NOT an entry level bike... I have finished 11 twenty-four hour mountain bike races on it. My back doesn't hurt and my hiney doesn't hurt after 24 hours in the saddle. This is very easy on my old body.
angela
