I can't decide between Hulkenberg and Ricciardo, but ultimately went for Ricciardo, based on his performance last season. You don't beat a world champion like he did last season unless you're WDC potential at the minimum.
Having said that, Hulkenberg's consistency since the latter half of 2012 has been phenomenal. He hasn't had an opportunity similar to what Ricciardo had, but he's beaten all his teammates convincingly and consistently, and that's all he can really do, so Hulkenberg's right up there as well.
Rosberg's margins with Hamilton aren't that stellar when it comes to races. He can compete with Lewis in qualifying, but when it comes to races, there's something missing. Sure, his points have been close to Hamilton, but that's because Merc always end up 1-2. The sheen's been nicked off him a little bit.