I agree with those who are still going to wait just a bit longer before making a decision between their voices. In the album, my favorite solo was Ayano's, but that could partially be because she got lucky getting a song that worked well for her (in comparison to the other two). I know that Megumi's voice is good, and despite how she fared with her solo, I'll still consider her my favorite at the moment. I do prefer Hiromi's looks when in Shangri-La mode though, by the way.
Megumi for me. Cuz she's the most "innocent" of them. Ayano is just annoying! What a bitch. Hiromi is cool but I don't really know anything about her. Her new DVD looks good though.
Hehe, I don't know about Megumi seeming innocent with what I've seen (unless you mean "innocent" by one way I can interpret it

). As for Ayano, do you mean by the characters she's played in dramas, the general impression she gives you as a whole, or did you by any chance actually meet her in person? :p
Oh, one more thing. I love the deep parts in SUPER HIGHWAY (like 0:52), so brownie points to whoever that is...
I'm going to guess that it's Hiromi leading at 0:50-0:52, and 0:53-0:57ish is Megumi (whichever one you might mean). Of course, I'll admit that I don't know their voices too well at the moment as I don't listen to them very much.