Svetlana I don't really like. Too harsh. Nickname sounds like 'sweater'. Sounds kinda stuffy, or perhaps like a depressed 60 year old Siberian nurse.
Had to chuckle at the "sweater" association. The root of Sveta/Svetlana is actually the word "light" as in, let there be... Back in Russia, I met a Svetlana who went by Lana, but Sveta is the most popular nn.
OP, I like both Svetlana and Ekaterina, but prefer Ksenia to Oksana.
ETA: my smileys were eaten by the phone...