I like both names. I really love
Delaney, it sounds a little more fresh and lively than
Sylvia.
Sylvia seems older than
Delaney, but it is also more classic. If you were to go with
Sylvia I would change it to
Sylvie because its spunkier. I agree that
Sylvia Delaney or
Delaney Sylvia would be nice combinations depending on which name you choose for the first.