Sibylla is too fancy for my taste and I'd say it with the emphasis on
BILL, so I'm not thrilled by it.
Sibyl is more my style.
I like
Isidora pretty well, and I'm gratified to see it spelled correctly. I dislike the
Isadora spelling lots. I think the only other thing (besides the ubiquitous misspelling) about
Isidora that keeps it off my list is that I don't care for the male name
Isidor /
Isidore.