I'm not a huge fan of
Dagny or
Daphne, but I can kind of understand why people may prefer
Daphne. 1) It's more recognizable (thanks to Scooby Doo, lol) while most people have never heard of
Dagny, and 2) the F sound softens
Daphne while the G sound in
Dagny is a bit harsh/abrupt. IMO.
:)