If I want to go on super fast and thrilling roller coasters, I'll hit SF. Let's face it, WDW has a few good coasters but nothing like SF. I went on the Superman coaster at Six Flags NE last summer and I guarantee that nothing at WDW even comes close.
However, if I want to vacation with my kids, WDW is the place to go. As much as I like fast coasters, I'd pick WDW over SF any day of the week. I would be happy at WDW just walking around, not even going on the rides. There is a special ambiance there that SF totally lacks. I haven't been to another theme park that even comes close. The closest is probably Busch Gardens in Virginia.