I had the 18's on my E350. One cracked rim and two bent ones. The 17's weren't as bad, just two bent rims. I got the 18" tires at Costco, they seem to run a sale every 2 months where it's a $70 rebate on Michelin and 1 cent installation. They just have the $70 rebate now. Got a set of 18 inch tires for slightly under $700 installed with a 5 year road hazard, free rotation and balancing. Had to wait a few days for them to come in as they didn't seem to keep that size in stock. For the 17's I got Purecontacts, but the price seems to have gone up a little, they used to be $126 a tire. You could get the contiprocontacts which are $133 or the general Altimax which are $120 a tire. They get decent reviews on other car brands but don't seem to be that popular on a Mercedes.
http://www.tiresdirect.net/TireSizeS...atio=45&rim=17
Also you can get the old bent rims bent back. Local guy around me charges $95 a wheel. Most tire shops should know someone who bends them back. Or check the local yelp reviews.