If I had the opportunity to choose between a Topps Chrome card and the same card stamped with National Convention on it I would definitely choose the NC card simply because I don't see as many of those and it would be easier for me to find the regular card in the future. I've never been to a National Convention but I do have cards in my collection that have been there.
My Huge Wantlist: http://www.zeprock.com/WantList.html