Get the car you like best and don't worry about resale. You're buying niche cars that aren't as easily resold anyway.

Never buy a car in its first year of production so forget the TT or forget buying a car for a year.

So go for whichever you like more, the SLK or 350. Enjoy driving it, take good care of it and learn the feel of it until it's like second nature.

I'd go for the bimmer!