My AFMrSE is probably the most played game in my collection, just because it is that much fun and doesn't really get old. The MBrLE is still getting quite a bit of play since it is still new to us. The light show is amazing on it, and the playfield, toys are beautiful, callouts and music are great. I do see it starting to lose its attraction since it is relatively easy to get far, but AFM isn't really a huge challenge to get through Attack Mars - though Rule the Universe can be a challenge and is still highly rewarding when someone gets through it.
If I had to choose between AFMr and MBr - I'd probably keep the AFMr just because it has more staying power.