McCain is FOR gay marriage, Rudy is against it.
Actually, I believe McCain was against the federal marriage ban, but he supported a proposal to change Arizona's state constitution to ban gay marriage. Rudy is very open to gay rights with the sole exception of calling gay civil unions "marriage".
Please do not misunderstand. I am NO fan of McCain whatsoever. Your point about Rudy's WOT stance is a good one and gives me pause about my initial response to the hypothetical of them being the two main primary choices.