Absolutely Zack Ryder, though Robbie E isn't bad at it. Ryder has the right amount of balance to his gimmick, I think. It's very obvious that he's a guido, he's the Jersey Shore guy, so on, so forth, but there's a layer of seriousness beneath it that transcends that part of his gimmick, so that he's much more than just a caricature, he's a serious wrestler, a young guy with a heart of passion and a dream to be champion. He has found the beautiful level of balance between going too over the top and being too generic. He's different, intriguing, interesting, and passionate, and that's why he does his gimmick so well, and why I legitimately believe he could be a world champion with this gimmick, and I'll defend that point gladly.
Robbie E, meanwhile, goes a little too hard to the over the top side, with so man Jersey Shore cameos and interactions, and never really innovating the gimmick. Robbie hasn't really changed at all since his debut, he's just changed his surroundings. He feels like a midcard caricature, because that's exactly what he is. He hasn't struck the balance that Ryder has, and he can't go beyond his own gimmick. He's a great midcarder - but that's it. Ryder has found something that can take him beyond that, and that's why he does this gimmick much better.