We ate at both places on our July 2006 trip. We had Tony's during lunch, and Mama Melrose for dinner (seperate days). I had read all the bad reviews about Tony's prior to dining there, but we like that type of food so I was okay with trying it anyways.
We liked Tony's much better than MM. The service was friendlier and faster (maybe just the time of day we ate at each location?). While our waiter at MM was nice enough, he seemed to disappear from time to time and we found the service to be slow. I really liked the decor of Tony's as well. I had two totally different types of food at each restaurant, and both were fine, but I can't really compare which was better.
On our upcoming trip this December I am really trying not to repeat any places we ate last time (except LeCellier!) just for the sake of trying new places.... but we still have one open spot so we may very well return to Tony's!
Just a side note, we find Italian food at WDW to sit very heavy and leave us feeling very blah, esp in the July heat! If we do it again, it will probably be for dinner rather than lunch!