Quoted from twenty84:

I owned a MMR LE and sold it fairly quickly. It really doesn't have a lot of depth to the code, and although the castle toy is really cool it wasn't enough to keep it. The shots were good, but it is a standard fan layout similar to AFM and Met - both of which you have and have better rules. Some of the MMR had play fields with insert text that was barely readable so you might want to look closely at the one you buy. For me the joy of playing the original 20 years ago was never recaptured.
The code in BM66 was slow to develop, and some are still bitter about the early code but today it is perhaps the best in any game available. Unlike MMR there are a lot of ways to play the game and a lot more to see and do that make it more attractive in a home collection. The turn table has to be level for it to play well, and it seems that is rarely done at the factory, and I think this contributes to the feeling of clunk people complain about, but I'm not sure what people mean by that. I have heard of node boards failing but it seems rare and Stern seems to replace them for free. There are a lot of cool mods for this game, so a discount on used one with them installed could be more attractive than a new stock game.
I can see the argument for MMR winning on shots/layout and toy (castle). BM66 has a lot better rules, sound, display, and lighting. I resold my MMR for what I bought it for, so it is hard to say it was a mistake. BM66 has been a long term keeper.