We've done both and CM twice for breakfast. Chef Mickey's is the best character meal we've done. The most convenient and fun, the foods good too, and we love breakfast.
Liberty is a treat, we actually did it by accident. We walked in on our first day ever at WDW and asked for table, and our luck took about 4minutes. That's special. When you get something you didn't expect.
If I had to choose, it would be CM. The reasons?, Mickey, Minnie ...