I like
Izolda best (though I do prefer
Isolda).
As for the others:
Urania - well, there's the obvious UR-anus problem, there, and Nuit sounds like a bird call.
Isis and
Gaia are pretty, just the mythological connection seems a bit heavy - maybe overpowering? - with them. I like
Anka, too, just not quite as much as
Izolda.