There probably isn't a fighter in MMA history who I would favour against Cain Velasquez. We may very well not see one for decades. He's a one-of-a-kind talent, and he could very well be the best MMA fighter of all time. I think that if that fight happens, the winner deserves to be known as the best mixed martial artist of all time. May be a bit premature to say with Cain's record, but he's already the best heavyweight in UFC history, he's utterly dominant, and he will have beaten Jones, which is an accomplishment that only the Hammer shares with him.
The truth is, as much as I respect Jones' skillset, and as elementary as Cain's is, how does Jones stop it? Even if you can stop Cain's takedowns, you have to worry about his boxing. Even if you can stop his boxing, you have to worry about him pushing you into the fence. From there, he may be the most devastating fighter in MMA. He's strong enough to hold you there, conditioned enough to grind you down, and he alternates from level changes to hard punches to the head. The guy is a freak. I still don't think people know how good he is. I've thought for a long time that he's the best talent we've ever seen, and he has, in my opinion, exceeded that talent and become the best fighter we've ever seen.
I'll get off Cain's balls for a second and point out that we don't know how Cain will react to Jones' kicking game, so the fight is at least interesting.