I like Celestine Soraka better, though if you play Janna a lot more I'd get Frost Queen.
They're both really nice skins (I have both of them). I'd personally go for Celestine since Soraka is my favourite champion and I have a fetish for light-themed stuff, but as for you, it really depends on your preferences.
i personally perfer Reaper soraka the hair on celestine soraka is awkward