Both games are great, but I'd honestly go with ToM. Here's why:

AFM is great, it's got a great ruleset, fantastic modes and a thrilling game experience. However, from my experience with the game, it does get boring quickly. I remember playing it the first time and getting around 13,000,000,000. I felt like the a pinball God. I thought it was luck, played another game, got just over 14,000,000,000. I don't get less than 10,000,000,000 now, and I've only played AFM about 50 times. It's too easy. Center shot, powerfield down, kill the UFO. Exactly the same for Wizard Mode. There's no variation to the game. Sure, there are the other modes, but the point is that the main mode is TOO easy to get through. Besides, I'm not a big fan of the playfield. The artwork is great, but there is a serious deficit of toys and gimmicks. The only thing marvelously unique about AFM is that it has the UFO LED mod, which actually requires an additional board.

ToM, on the other hand, my favourite game. I'm hoping to get my dirty paws on it soon (either that or TAF). It's such an adventurous game, honestly never gets boring. It also requires quite a bit of skill. I mean, fair enough, you can get through the modes anyway even if you miss the skillshots, but if you can master ToM you'll honestly have the time of your life playing this game. Modding capabilities are amazing, the game itself is wonderful (rated #1 by me, die-hard JPop fan), ColorDMD support, looks sick as tits with LED lighting. I only managed to break the 1,000,000,000 highscore after about 30 games.

ToM over AFM anyday, although I love both of them.

Pfff... try Berkshire Hathaway.