Miranda was very popular as far as I recall. Her thread was a on the biggest with Liara, Tali and Kaidan.
A character thread isn't the only thing I take into account to see if a character is popular or not. I read the Miranda thread everyday, and it was basically the same people talking over and over on ton of pages about everything about Miranda. There were many threads complaining about Miranda, many vocal haters, many thought she was boring, didn't like her arc story with " I'm not perfect ", mocked the camera angles on her butt, called her Michael Jackson, etc.
Also, in a character thread, you could have just 30 talkative folks, and the thread could move very fast everyday. The tone overall on the Mass effect board for Miranda was very negative, while it wasn't the case with Tali. Overall, almost everyone liked her, even if people weren't her fan.
I've been in many mass effect forums, and on internet, Miranda was really bashed, while Tali got all the love no matter where you were. And the Tali fans were legions.
Miranda is clearly popular, but more with the silent majority, or people who don't give much their opinions about her, but the hatred seemed very strong with the hardcore fans.