I don't like
Casey at all.
I love
Cecily; I would use it as a fn or a mn, and I would be happy as a
Cecily myself.
Cassandra contains
Sandra, which is drab and dated, and the Trojan War reference is tragic. Don't like it; don't enjoy
Cass or
Cassy either.
Carmen isn't bad. The opera is a delight, though the heroine isn't. Nice to have a mezzo in the leading role. But the appearance of the word is unfortunate: car + men sounds like a bunch of mechanics.