Munsters is easier by far. You can easily start multiball by hitting the main toy. It's a pretty forgiving game and scores can be very high. Completing the characters is pretty easy so you can get to the wizard mode quickly.
That said, I wouldn't recommend Munsters to anyone. The code is too shallow and, in a home environment, I think it will get boring fast.
I have an Iron Man and owned Tron. Both relatively shallow games that are challenging and keep you coming back. Munsters lacks the challenge and excitement of getting a really good score.