Topo, I've never lived in either city but the trucking company I've driven for for the last 10 years is headquartered in Chattanooga and I deliver to Meijer (a Walmart competitor) stores in the Louisville area. I like both cities very much.
Chattanooga is much more hilly than Louisville. (Just North of Chattanooga on I-24 is Monteagle; one of the the largest mountains in TN. Would be a consideration if you drive to Nashville often, especially pulling a trailer)
Both have very nice areas as well as the typical "inner city" areas. I see "sprawl" a little bigger possibility in Chattanooga as the I-75 corridor to Atlanta builds up.
Metro Louisville is a growing area, as well, but you may be able to get away from the city a little easier if that's your goal. Louisville is, of course, the larger metro area. One thing that attracts me to Louisville is , despite the normal "rush hour" that cities have, it has a good number of alternate freeways to get around backups on. Most of my store deliveries are during the a.m. rush hour and I rarely get stuck in traffic (thanks to a c.b. radio and a wonderful oldies radio station with good traffic info
) Hope this is a good start for you; Best of luck!