Heard all the previews, here are my thoughts...
Futatsu no Tsuki: So this is what a Takane song sounds like. Gotta say, I am highly impressed with her vocals. Can't wait for the full song.
Nostalgia: I hate to say this. I mean, I REALLY hate to say this, but...... I think Miki's is the worst of the bunch. Not because its bad, but because I think the vocals particularly hurt this song, imo. Miki sounds too high-pitched here. If she sang this song like she did, say, "Marionette no Kokoro", "edeN", or "Tsuioku no Sand Glass", then I would instantly have fallen in love with this song. But where it stands right now.......eh. :/
Suteki Happiness: Typical Haruka. Cute, bubbly, and actually pretty catchy. I like!
Saihyou: Ms. Imai, stop. Stop having such a perfect voice!