Neither, get a MET. Depth and great shots Seriously though now as that wasn't an option, are you a mode based player or a score based player?
If you like the journey of going through modes then MM would be the better game as you have task to complete in order to get to the end. With AC/DC it's all about maximizing your scores by the risk vs reward of the game. All the songs are pretty much the same as you have to hit ___ number of shots to open the jukebox to change the song. I'm more of a mode based player but I prefer AC/DC over MM just for the adrenaline I get from playing it during a good game. Nothing beats having 100 million points ready to go and needing to hit that wide open right ramp that for some reason just shrunk drastically. Well, nothing but needing one more shot to get battle for the kingdom.
See what I did there? A lot of words that basically got you back to the start If it was me, I'd go AC/DC now. Play it for a year or so and then pick up a used MMr if you find AC/DC doesn't strike your fancy.