(Sorry, mistakenly posted in non-spoiler forum first.)
Two possibilities. I'll eat my hat if it's not one of these.
ii) A new character, specifically one of the two people seen walking over the hill at the end of Season 2. (These people aren't Christa and Omid- if they were, it would be completely anti-climactic.)
So why Christa?
i) She's a leader/doer type person. She clearly wears the pants in her relationship with Omid. Her active, physical and concerned nature would make her a natural fit as a PC. If Lee hadn't been there, she would've been the boss of the group no question.
ii) Omid is too jokey and a bit of a wuss compared to Christa. This isn't Monkey Island. I don't see him as a PC.
iii) She's a woman, making for a change after Lee.
iv) The big one: she's pregnant. I think we can imagine how messed up it would be playing Omid and having to protect your wife and unborn child in this crazy zombie world. Well how about *being* the pregnant woman? Over the season, expect Christa's pregnancy to become more of an issue, almost certainly climaxing in a birth during terrible circumstances as you/Christa fights to save herself and deliver the baby at the same time. This is exactly the kind of messed up situation the Walking Dead Thrives on.
Of course I could also imagine a situation where Season 2 is a completely seperate group of characters who meet up with Clementine at the end, and then Season 3 is a so-what-happened-to-Christa-and-Omid scenario, which dovetails with both of the previous seasons.
Why not Omid?
Why not Clementine?
Expect Clementine to be a PC in the inevitable Season 3 or even later. Being her now would rob the ending of Season 1 of its mystery. We won't find out what's up with her immediately. Also, as many have commented, the ending of Season 1 tells you that what Lee says to her as she dies will affect her actions, which doesn't make sense if you're controlling her.
Why not Molly?
As many have said, she's too kickass. This isn't an action platformer. Leaping over buildings being a ninja and killing every thing would rob the game of tension and danger.
Why not Lee?
I find this conversation ridiculous but I see some people insisting that Lee will return in a miraculous save. People who think this don't understand Kirkman's universe. He is dead, dead, dead, and never coming back. To "save" him would completely violate the TWD franchise.
What about Andre?
Actually not a ridiculous question. I would be quite surprised if he doesn't turn up in some shape or form somewhere down the track. It would be unlike TT to just never ever mention him again. Similarly, we may also learn of what became of Vernon, though unlike Andre, Vernon would definitely not be the PC.
And on an unrelated note that doesn't need its own thread, I think it's a real shame that everything keeps focussing on one corner of the Southern USA. There's a huge untapped potential in what's going on in the rest of the world. How about Iceland? South America? Africa? New Zealand?
(I could see a storyline in an exodus north to either extreme Russia or Canada, where the walkers freeze and become immobile, but it's still hardly peachy keen due to the difficulty of surviving in that environment. Be interesting to see how the inuit are doing.)