I prefer
Emily to
Emma and
Emerald to all the others.
Emmerson I think of more as a boys' name, but wouldn't use it on either.
I've met Emmas and Emilys of varied ages, but an increasing number that I meet or hear about are younger. My old roomie has a toddler named
Emily and one of my old campers just had an
Emma this summer (don't know mns off top of my head).. I know an
Emily Rebekah who's 11. A few Emilys in their 20s and 30s, but not so many... One is
Emily Joyce and has a friend named
Emily Dianne.
Honestly though, I think
Emerald is the prettiest of the bunch.