We have tried both, IMO Hollywood and Vine is not a very good buffet with nothing else special about it. We did Mama Melrose last year and we enjoyed both the food and the atmosphere.
I would have to choose Mama Melrose. We ate at H&V a few years ago and were not that impressed. It is just your standard buffet food nothing special. If I wan't to eat at a buffet I will go to Boma at the AKL. It is by far the best buffet at WDW. Now back to Mama Melrose. We last ate there last December and we really enjoyed it. The food and service were excellent. We have ate there many times and except for one meal we have always enjoyed ourselves. We also enjoy dining at the Brown Derby and 50's Primetime while at MGM.