The only one that meets any conservative criteria on this list is Thompson, I will make an exception to my remark for Tom Ridge, not knowing much about him. Mitt, Rudy and Joe are not conservatives and will hurt McCain more than he is already hurting in the eyes of conservatives. I find it interesting that Duncan Hunter's name isn't on the list, as well as several other people I could think of.
Ridge is a pro-abort Catholic, a 100% no-go.
Joe is also “another old guy” so you don’t have to worry about him.