Stannis, as he's the only claimant who'd be even marginally competent as a ruler.
(Also, Davos Seaworth is my favorite character in the entire series.)
More or less this. Robb is a great leader of men but we saw where that gets you absent administrative tact in the person of Robert Baratheon. I don't share the hate for Cat but she's, shall we say, less than an ideal advisor. If Robb had better help I'd probably support Northern independence with Stannis ruling the Southern kingdoms. The Ironborn have an extremely good case for independence, culturally speaking, but said culture is such that an independent Ironborn nation-state would from a realpolitik point of view be undesirable for pretty much every non-Ironborn on the planet within reach of saltwater. Also Balon is a bit of a cock even by their standards.
Renly is a toom tabard and Joffrey is one of the most disgusting people ever.
The Onion Knight is wonderful, although the nickname makes me think of a certain minor character from
Utena, which is a little arresting.
Dany is great and admirable in many ways but has some of the same problems as Robb for reasons that become apparent later on.
I should point out that I've read the books so I know how this plays out, but hindsight actually doesn't change much in terms of who I personally support.