For my family, I think I would have to say Soarin.
I don't even know how many times we rode it. The park was so dead we just kept getting back in line and riding again! Finally we had to tell the kids enough!
If I had to narrow it down, I could easily ride Expedition Everest over and over and over again. I actually did do this for about an hour or so during AK's EMH this past December No waits!