I like
Sylvia a lot better. It's an older name that's coming back into fashion, it flows beautifully and will age well, but can also be shortened to the cute
Sylvie or cool Via.
Delaney sounds much less nice to my ear and I admit I find it a bit awkward to say (and yes, I have met a
Delaney in person). Not that it's complicated, per se, but it just trips me up. That, and I don't think nicknames
Laney or
Lane are attractive.