Esther is a so much better. I don't know any girls called
Astor but I know one
Esther who is 21.
Astor makes me think of the male name Alastor and it sounds like a surname.
Esther soudnds like a classic old fashioned and beautiful name, so yes I get a very different feel from them.
The difference between
Astor and
Esther is certinately big enough. I wouldn't use them as sisters or anything, but I don't think people would get mixed up. Especially because
Esther isn't REALLY popular.