I really love the long u and oo sounds. Euphemia, Eugenia, Eudora, etc.
Oona, Luna, Lucy, Louisa, etc.
I also like girl names with an "or" sound, like Cordelia, Cora, Georgia, Leonora, etc.
I tend to like girl names that end in -a.
I also like names with long i, like Simon, Ivy, Iris, etc.