Go and watch more of Seth's work. Watch his FCW work, his ring of Honor work. You've basically come into Dean when he has just recently become a good wrestler and not just a good entertainer. In ring Seth his in my opinion miles ahead. More well rounded, more technically sound, better high flyer, better grappler. Ambrose is good in that he can tell a story in ring, but comparing his technical proves to Seth is in my opinion hard.
Seth comes out of Ring of Honor, who put a lot of value in great technical skills, he's been molded from wrestling guys like Daniel Bryan, Austin Aries and Nigel McGuinness, some of the best talent to work the modern age of wrestling. Dean comes from CZW, one of the most violent but also most botch heavy federations out there. Dean before FCW was nothing but a brawler, a brawler who could talk but a brawler non the less.
Dean is a more well rounded character than Seth, but Seth as a wrestler is much better.