Alberto Del Rio is easily the best heel in WWE, with the exception of CM Punk (if he still is a heel ? ) Del Rio brings it on the mic and the ring, consistently performing at a high level pretty much every week for the last year. Yeah the Miz is good on the mic but his in-ring work is crap. That along with his promo style/character make it hard for many fans to take him as a legititmate main event player. Del Rio puts on great TV matches with the top stars all the time. Miz will bust out maybe one "good" match like every couple months. Miz may draw a little more heat than Del Rio but some of that is b/c Miz is generally not liked to begin with (x-pac heat). Outside Punk, I dont think anyone has worked as hard to warrent a push than Del Rio. Although I didnt necessarily agree with how fast he got his push, he took the keys and ran with it. In contrast to Miz, who didnt produce anything of value in the ring before he won the strap, Del Rio's fueds and matches with Mysterio and Christian were some of the best of the last year. His match with Edge was a pretty strong showing for a relative newcomer. Id say with good performances and wins over guys like Edge, Christian, Mysterio, and Show, WWE has done a good job to build up his resume as a legitimate main eventer. This along with his promo work being among the best warrant Rio's push.
