I would say that most of the current themes are pretty terrible.
A great theme needs to be memorable and it needs to say something about their character. It's no surprise that most of the greatest wrestlers and the greatest characters in history all had great theme songs.
If you don't remember or if you can't hum the song after the first time you hear it, that's a sign that you have a bad theme song. If your theme song doesn't garner any kind of emotional reaction, that's a sign that you have a bad theme song.
If your theme isn't distinct and unique, that's also a sign that you have a bad theme song. Which means in 2014 if your theme song is just empty guitar riffs or some bland generic alternative rock song you forget the first time you hear it (bland generic hip hop song if you're black)... that means that you have a bad theme song.
I'd say of the current lot the best themes belong to Cena, Bray, Swagger, Funkadactyls, Fandango, Santino, and Del Rio. Those are the first few that come to mind because they're either distinct or because they help round out their character.