Yes, Mashiro is cute but let's leave that on Sakurasou's discussion forum okay?
Now about Asuna, it's already a common fact that people tends to love the characters which were introduced first. This, is mostly because of the tendency for people to create a shipping, or a whoXwho couple as an OTP for their imagination so it's understandable why people like Asuna so much (Reki wrote this while focusing on the romance between her and Kirito).
Suguha, who now has been introduced in the anime is also gaining her popularity in a flash because ALO is mostly centered round her while Asuna is playing the trapped princess role. Of course if we're talking about background Suguha would be more interesting due to the incestuous love and the adoptive of Kirito while Asuna's was just that of an accident in trying a game (Shino's is better though, but that's another story.)
Now I'm not trying to bad-mouth Asuna in here. I'm one of her huge fan (as seen in my signature) but since we're talking about stereotypes in choosing popular anime girls it's only fair that I shared my opinions on this matter as well. Rest assured, if Asuna and Suguha entered a contest after ALO is finished I'm sure they' could end up in a draw (or Suguha might steal the glory. Who knows?)