I liked Villopoto more than I liked Dungey. I mentioned Dungey in order to bring an example to help anyone reading getting a better idea of what I was saying
However since you mentioned it and since I like American motocross almost as much as I like MotoGP I'll be going OT and give you my opinion.
Talent, speed and technique wise there's no comparison. RV > RD and honestly that's not debatable IMHO.
I only reckon Dungey comes off as a more chilled dude, which brings us back to the example I made above about sponsors loving him. Dungey had that "I'm just a nice kid" appeal, nothing could touch him like you say.
RV wasn't more emotional, he was simply rawer. Kinda like Casey.
We are anyways talking about two amazing sportsmen, I'd like to underline that.