Barrett IS a great option to be a top guy. He has this presence about himself, and could possibly be the next mega heel in the vein of Triple H.
Barrett actually has been built up to some extent. While he was depushed down to the midcard after Nexus, he didn't end up losing most of his matches. He was always kept very strong, it's just that the quality of opponents changed. He went from fighting John Cena & Randy Orton to fighting midcarders, but he wasn't constantly losing week in and week out like The Miz.
That's not the point. All I'm saying is that, if Ziggler hasn't done enough to be a top contender, how has anyone else aside from Sheamus, Show and Orton? Ziggler actually wrestles top-quality matches, is better on the mic, and has the attitude of a cocky and conceited heel.
Sandow is awesome, but he shouldn't even be mentioned, unless we're going to consider Cody Rhodes again.
Barrett will do about as much as ADR. Both are annoying on the mic, both can't really find a place into a decent storyline now, neither wrestle exciting matches, and Barrett now possesses one of the worst finishers in the business.
It would be a shame to see Barrett get title shots before Ziggler, but it wouldn't surprise me, since we've seen Jack Swagger and Khali as champs.