I think that the "Hate" for Cena was exaggerated by the fans, he was the guy that the fans boo'd but deep down a lot of people cheered for him, but because it wasn't cool to like him, they boo'd. With Roman the dislike of him is real and visceral. Cena comes across as a pretty good guy, who loves the business and loves entertaining, and does a ton of charity work and other stuff. He's also a complete dork. Roman's whole vibe is arrogance and entitlement.