Sasha: this seems relatively fashionable, and easy for people to say where I live. And I like it. I do not like it much for guys unless they are Russian, but I think it makes a good name for a woman or girl who isn't Russian.
Masha: I don't think this works well for English speakers. Too much of the word mash or mush in it. I like
Maria.
Natasha: this seems dated to me and liable to lead to the nickname
Tasha, which I don't really like.
Natasha is alright though. I like it more than
Natalia, barely.
I'd use
Alexandra with
Sasha as a nickname, but I think
Sasha can stand on its own as a full name, about as well as something like
Sandra can.
- mirfak