I had an aunt named
Eva. It wasn't a family name, so I asked my grandmother what the reason was, and she said it was because she was their first child. I paused to ponder a potential Uncle
Adam! And she went on to explain that they liked the fact that it couldn't be shortened (this from the mother of a
Beatrice ...) just as my aunt came into the room and offered to make tea. Gran's answer, in total innocence: "Thank you,
Eve".
I like
Eve a lot, probably because I had a good friend at school who is actually an
Evelyn but has always been known as
Eve.
Eva ... no offence to my aunt, but it makes me think of the way -a endings were suddenly so very fashionable in the 18th century -
Lucinda instead of
Lucy,
Maria instead of
Mary,
Amelia instead of
Emily and so on.
Eve seems more energetic as well as prettier.
Not being American, I would not presume to predict anything about name popularities there.