I saved Carley out of gratitude and respect for her selflessness.
- She rushes out of the drugstore's safety to save me, Clem, etc. (complete strangers).
- She stands up to Larry and Lilly who don't want to take in strangers.
- She opposes Larry killing Duck.
- She saved Clem from the bathroom walker.
- She keeps your secret. In a way, this saves your life again because it prevents your past from being used as an excuse to kick you into the streets full of walkers.
- She volunteers to go with me to rescue Glenn.
Did Carley being a pretty woman had something to do with my choice at a subconscious level? Probably, I don't know. My first instinct was to save whoever saved me. This was the same reason I tried to save Shawn over Duck at Hershel's farm because him giving me a ride saved Clem and my life.
Like others pointed out, she had a lot more screen time, and all that screen time was mostly about her helping me. It's hard to dismiss that.
Personally, I was not impressed with Doug at all. Carley haters like to criticize her for the battery thing while ignoring the good things she did. Seriously, who here hasn't done something that's stupid and minor? They also ignore that Doug doesn't act very smart either. I mean he suggests going outside and taking a look hoping a flimsy store gate will be enough to hold back walkers. The only reason the pack of walkers didn't see you in plain sight was because TTG writers willed it so and made chilling out side the drugstore necessary to forward the story. Logically, it didn't make sense and was a pretty stupid and dangerous move. I also don't recall Doug standing up for the newcomers during Larry's tirade.