It has to be Carolina. Tex has killed an army of crazy noobs in twice the time it to CA to kill an army of well trained guards and an ODST. And it took Tex 3 times as long just to incapacitate blue team and Tucker.
And let's not forget Tex got killed by an alien, and Red Team twice.
We don't know if Carolina has an AI in the little that we've seen of her, her kickassness might be because she's one of the first Freelancers to have an AI. Also the two can't really fight without an AI considering that Tex is one. And for anybody who say she isn't, then if she's a ghost then Carolina couldn't win (or maybe even have) a fight anyway.
The red and blue noobs didn't, and even if they did they come back to life anyway, so if there couldn't be a restriction has to how many she could kill. And it's up to debate as to whether or not Crunchbite had such plot armor. Ya, he was important to the plot, but the plot wasn't important.
Carolina, didn't church give some sort of speech in the last couple of episodes of last season about how the current Tex was "designed so that she would be incapable of winning" or something along those lines.... It was after her fight with Wash and the Meta and she was put inside the A.I. containment unit.....Please forgive me if I misunderstood said speech
Well Carolina isn't still walking around because of the whole 2 AI thing. I'm sure Tex wouldn't be able to cope with that if it happened to her too. Then again, Tex isn't technically human, so who knows...