I use an OEM set of centercaps on my summer 18"'wheels, but bought some replica caps off eBay to use on my winter 17" factory wheels, and can honestly say that after a full winter season of salt and snow, they have held up beautifully. They look almost as good as the OEM ones. Here's a pic of the replica caps:
At $40 shipped, they are a bargain, and you can buy 4 sets of them to one OEM set.
Here's the seller. No affiliation...just a satisfied buyer.
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=130411082674&viewitem=