No matter what you do - don’t buy a new game if you don’t like the theme, especially at today’s prices.
Game play wise there is no comparison between the two. But if you don’t like the Batman theme as much as Munsters, maybe Batman isn’t for you. And in the Munsters case “theme” also specifically includes the title music theme. You will hear that a lot. I love it, but it may drive some crazy.
For me to consider buying a new game I have to like the theme, the art, the shots/toys, the game play, the audio and video and how well everything works together. In the LCD era that’s more difficult to do at launch because software (including A/V assets used) are rarely close to the ‘finished” level. It’s even tougher if you want to buy a Stern LE because you usually have to decide before you have ever played (or even seen) the game.
I don’t rotate or swap games frequently. If I buy one I expect it will be in my collection long term. Sometimes that doesn’t always work, but because of space constraints I have to let a favorite go to bring in another game. In your case, it’s one game. Part of the consideration in that case is how long will the game hold your interest.
Both are good choices. But if you like the Batman more (or about the same) as Munsters, it should be a pretty easy choice.
Let us know which way you decide. Then make room for another machine and get both.