Neither is likely to break since they are new games but the trolls on MM are the most likely mechanical failure IMO. I also really don't like that on MMr they put driver transistors mounted under the playfield. In AFM they moved them to a board in the backbox which I like better. that being said, there are MMr's on location that have survived a lot of plays with little to no failures of electrical components. Also the first AFMr I saw on location had a trough opto problem and probably had less than 1000 plays on it so as with pinball, you will have to fix something at some point. Pick whatever game you like better and if you aren't sure which one you like better, go play them on location if you can.