It depends on what you want to do with it and the price.
If you want a "Go-Everywhere" r/c that can jump, pull wheelies, drive over everything in it's path, go with the MT.
If you are looking to get into racing whether it be in car parks or grass/dirt the Marder is a good choice.
The Beetle is a Marder, but with a VW body on it.
I own both an MT and a buggy, I would say I have more fun with the MT. It's slightly wider (wheel offset) so it doesn't roll over as easily.
The good thing is, it doesn't really matter which one you choose, as they are all based on the Marder buggy chassis and can be converted to each other. Meaning a Marder can be turned into an MT and the MT can be converted to a Marder. I would say buy the one that reaches out and grabs your attention the most, or get the vehicle that most closely resembles the vehicles of your mates. Or the vehicle that is completely opposite of your mates r/c's to be different, whatever your personality is.
The great thing is there are tons of aftermarket parts for the FG's and you can make it however fast or cool as you want.
Check out some Youtube vids and see which you like the best.
If you still cannot decide, go with the one that's in the best condition.
I cannot comment on the Lauderbach as I have never owned one.