what is harder on the suspension and ride is the weight of the tire/wheel assembly....typicallly the smaller the wheel, the lighter the assembly, but there are some really heavy 18's and some really light 20's (and some really, really heavy 20's)
depends on what style you like...might want to find some used take-offs on craigslist....or go new OEM, or go aftermarket. personally, I'd look at these wheels, which are the OEM wheels on the 2009 challenger rallye's
reasonable price, good looks, OEM quality, and these are actually made in the USA....
if you're looking for a good all-year tire that's awesome in the snow, get the Nokian WRG2 SUV's in 235/55R18 or 225/60R18