I was leaning Orton at first, but many of you made good cases against their feud lacking bite despite their history and number of matches. I'm torn between Edge and Punk. Both brought out the best in Cena and had very memorable moments. Punk was the more formidable opponent, but Edge was a perpetual thorn in Cena's side that made things personal.
I don't view Brock as a true rival to Cena, because he beat the shyt out of him every time that they faced off. Even the Ectreme Rules matched was dominated by Lesnar and ended in fukkery with Lesnar beating himself more or less.