Re: Out of these 3 matches which would be the biggest at Wrestlemania
Cena/Rock. They can both still go (well, one has to assume with The Rock).
Austin/Hogan would be fun promo-wise, but the match would be terribly limited.
As for Taker/Sting, it's a dream match of mine, but honestly I'm not sure how big of a draw it would be today given that much of today's audience probably doesn't even know who Sting is.