I like the idea of this topic so I figured I'd reply with some detail to keep it alive.
1. Moon Color Chainon. It's so damn catchy to me. It's the perfect blend of sad and cheery and that's why it works so well to end both Part 1 (where everything is going to hell) and Part 2 (where everything is fine again). I really like the lyrics, too, they hit that sweet spot between nostalgic and hopeful. I wish we'd gotten an actual opening to this, although I love the music video we did get.
2. Moon Pride, or should I say MOOOOON PRIIIIIDE, ANAAAATAAA NOOOO, CHIKARA NI NARITAIIIIIII~, because I can't think of this song without it instantly playing in my head at full volume. Really catchy, really good, and it gives a shonen energy to the first Crystal openings which I felt was fitting given how those arcs play out in the manga.
3. Eternal Eternity. The way the two voices blend together is awesome, the lyrics are on point, and the violins are amazing. Everyone seems to like this song and for good reason.
4. New Moon ni Koishite, the Momoiro Clover version anyhow. I admit I really disliked this song when I first heard it but, I mean, after MOOOON PRIIIIDE, ANAAAATA NOOO~ I got this low energy saccharine song and I found it really boring. But the second version vastly improved things and by the time the Momoiro cover dropped I really warmed up to it, they gave it the energy I expected from an opening. I could still do without the first version, though.
5. Eien Dake ga Futari wo Kakeru. I like the secret spy vibe of the rhythm and it's catchy enough. It's not my favorite but it's nice to listen to from time to time, and Tuxedo Mask posing in the video is hilarious.
6. Moonbow. I'm not gonna lie, I find it a bit boring. It's just not for me, but even if it's not I can tell it's a nice romantic ballad, just a bit slow for my taste.
7. Otome no Susume. It's like the opposite of Moonbow, it's too high energy and that makes it a hard listen. I still can't help but like it because whenever I do listen to it I'm reminded of that one episode that ends with Chibiusa dying immediately followed by this song's fanfare blasting at full volume, lol.
8. Moon Effect. I could never get into this song, it just has too much going on. The music feels like it doesn't match the vocals, which are too shrill anyway, and the whole thing doesn't work for me outside of the hectic final battle, and even there I feel that maybe dialing the instrumental pace down a bit could have fit better.
I'm looking forward to listening to Moon Flower to see where it ranks for me. Although there's a couple songs that don't do it for me, I've really enjoyed the Crystal music.