Brian,
I have the AMG sport wheels on my E350 and really liked the look. I couldn't find the same application available for the Metris yet, so I went with aftermarket wheels. The company is Rial, manufactured out of Germany, and the model is called M10. This is an inexpensive wheel and can be sourced very easily online. It's a 17x8 sized alloy wheel with 48mm offset. I did some research on tires and chose the Michelin Defender LTX M/S XL tires in a 225/55R-17 size (OEM sizing), based on ride quality, build, and reliability. I wanted to go to a 18" or 19" wheel/tire combo, but based on the curb weight of the Metris, needed to consider a tire with a C/D load weight rating to handle the weight.
Compared to the stock alloy wheels with my Hankook Ventus tires, I see a marked improvement in ride quality, quieter and smoother. I'm getting some compliments on the wheels, esp. since I have the OEM caps on them.
Good luck on your search ... hopefully, this has been helpful.
B