MM is instantly fun for anyone who visits, but it's pretty straightforward game if it's your only pin. Actually beating the whole thing is easier said than done, but it's not complicated. If you rarely have long stretches of time to play and want quick and easy games that you can master easily, get MMr.
TWD is brutal on new players, but deep rules that would last you a long time. If you plan to play a lot of pinball enjoy a little strategy and don't really care if non-pinball friends have much fun, get TWD.