Tahan, obviously.
I didn't even have a Tahan bias from the get-go. It kind of happened because of how straight-up she is. I love that she's a physically beautiful woman who also speaks her mind, because it's actually not all that common. Most pretty girls think it's enough to stand around and be silent, or not to try and listen to the other side. Tahan needs to mature, but she did sometimes try to see both sides of the coin. Her and Tully's friendship is a good example of how she manages to do that, because it was obvious she wasn't cool with what Tully was doing and let her know, but was still friends with her.
Mikkayla is also really pretty, but so insanely insecure. Her insecurity rules her, and I think Tahan got under her skin because she's 1 ) beautiful, 2 ) confident, 3 ) not afraid to disagree. That's a deadly combo for insecure girls. I wanted to like Mikkayla, but I just don't like insecurity. I wish she had just stood up to Tahan or showed she didn't give a shit, but instead she responded the way any weak, sad-on-the-inside girl would. She was also really nasty and gossipy, and while Tahan's attitude to her was brutal at times, Mikkayla just went about it the wrong way. I hated her whole thing with the "Sugar Sisters" (HATED BOTH OF THEM) and enabling Jade's stupid behaviour.
So, while you can't really compare them, there's a clear winner.