re: 16 inch rims vs 18 inch rims?

I have 18's. You can only buy low-profile tires which are much more expensive, but if you're into performance, have a few benefits.

edit: Obviously depends on what it's going on...I have a car so low-profile is only option with 18's. I'm guessing you don't need it, but finding low profile snow tires is a pain in the arse.