Unless Mark did something drastically different from Doug in the first Episode I'd still pick Carley. Even if Mark had a gun too I'm still leaning towards Carley because she saves everyone's lives outside the pharmacy and then in the store saves either Lee or Clementine's life, all before you even learn her name, and apparently in full defiance of what Lilly and Larry wanted.
Then there's the fact she knows Lee's past. I guess that's suppose to make me like her less, but I really appreciated her being direct and honest with Lee. She could have used it to threaten Lee, saying she'd tell the others if he did something she didn't like (like Larry does) but she gives him the benefit of a doubt and warns him to be careful about his past so as not to create another problem in an already bad situation, which also showed me she was pragmatic.
Now if it was between Kenny and Carley (in the first episode), that would be a hard choice for me. I'd probably have to go for Kenny, I'd hate to think I'd leave Duck without a father or Katjaa without her husband.