You may as well put silly money on an Undertaker/John Cena double.
As DQs and countouts are rare at Mania, you will also be safe placing money on Triple H, Ryback and Alberto Del Rio. As there has to be one or two heel wins you should be looking at Fandango, assuming his match with Jericho occurs.
Hell No is a tricky one. I can see either team winning and The Shield may finally go down, or win.