I'm obviously a little biased now, but I think 18's work just fine on these cars too. Don't get me wrong, I think you have to pay more attention to ride height and tire diameter to get the 18's to look right than you do with the 17's. I used to be firmly in the "nothing bigger than a 17" wheel camp", but the tire selection and improvement in tie rod end clearance made me go with 18's on the Duster, and I think it works.
17's work well too, I still think they're probably the best suited to these cars visually. And if you want to stick with a 255 wide front tire or narrower they work great because the tie rod clearance doesn't really come into play to get the tire to fit. To move up to a 275 in the front it makes life a lot easier to go with a 18" rim.