those 90s mtn bikes are cheap and plentiful and predominately rigid. all three qualities make them great city bikes.

we are all talking geared bikes by default, unless otherwise stated in the post (or thread title or forum subsection).

atlanta is pretty hilly, singlespeed would be a good workout. i have a '95 GT converted to SS for mtn biking. it's fun to ride, but it can be hard on the knees. i have not had a single speed bike for city riding... other than a huffy cruiser.