Welcome to the opposing poll to the "most masculine character". Obviously a "most feminine character" poll wouldn't work, as generally women in gaming aren't depicted as stereotypically feminine types in the way that men are depicted as masculine.
However! We can rate them based on how believeable that are. That is to say would a woman do what this character does, and if so, does this character behave herself according to how a woman would?
Of course it's all just speculation. We can never know how a woman -would- behave since everyone's their own person and everyone handles situations differently. But that aside, let's get to the voting anyway.
Again the disclaimer: I haven't played all games so excuse me if some characters are missing. The choices are as follows:
Elika, Prince of Persia
She's the loyal sidekick of the Prince, though sidekick is rather demeaning. She's about as crucial to his survival as possible due to constantly having his back, but there's no way that she could've accomplished her epic task without the Prince's talent in combat. As far as I'm concerned, a schoolbook example of what men and women add to each other.
Lara Croft, Tomb Raider
This is where it all began. The first mainstream female character in gaming. Perhaps a guns-blazing archeologist isn't the first thing that comes into your mind when defining "believable", but the latest Tomb Raider games seem to have gone to greater lengths to bring out her realism. Her physique has been refined to be less ridiculous, more personality has been added and she seems to approach her enemies and archeological findings with the finesse and care that only a woman would. Of course, some people will argue that the Lara we know from Tomb Raider I to IV was the best.
Cate Archer, No One Lives Forever
She may not be as recent a character as others on this list, but let's at least agree that she was about as girly as it gets in gaming. She has the 70's female look down to perfection, but then again, is it believable that someone in her role would be so typically female?
Samus Aran, Metroid Prime
I've never played a Metroid Prime game in my life, but that doesn't keep Samus from making the list. One thing about her is a given: she doesn't wear a suit that screams "look at me, I'm a girl!" like the rest of these chicks do. That alone is pretty believable. Of course, that might just well be where it ends? I'll leave that up to the experts.
Commander Shepard, Mass Effect
Hey hold on, wasn't Shepard a guy? Well, not really. You can play as either gender in Mass Effect. Due to it being the only RPG where the main character has voice acting, we get to experience some of the best female voice acting in a game yet. She has the balls that it requires to be an intergalactic commando, the femininity it takes to win the love of one of her male crewmembers. The subtleness and care it requires to be a true paragon, the
yness and hawkishness it takes to be a renegade. Of course the question is: would a woman ever have such an important military position, even in the 22nd century AD?
Faith, Mirror's Edge
Faith is just a girl. A girl who happens to be agile as a cat and can run like the wind. She's got the disdain for military regimes you'd expect from a woman and there's certainly no man who can jump and run as quickly as she can. Considering her job as a Runner, it's only natural she'd be female. Come to think of it, there really isn't much about her that we know of, that could be considered unfeminine. She avoids combat, dislikes weapons and cares greatly for those close to her.
Alyx Vance, Half Life 2
I've never quite played enough Half Life 2 to get a feel for what kind of a character she is. What I do know is that she's charming as hell and is gifted with a sufficient amount of wit and brains. She seems to display a great amount of care for the people around her aswell as her robot (who I forgot the name of. Wasn't it Dog?). There's not much I can think of that would make her unbelievable, but like with Samus, I'll leave it up to the experts.
I'm aware that there's female characters in other games aswell but I feel we don't get to see enough of them to accurately establish if they're believable women. Either their context is too extreme (Jaina Proudmoore, Warcraft), or they're represented by mediocre actresses in corny cutscenes (Command and Conquer and Red Alert).