I like Veronica a lot. It's got a lively fun-loving sound, but it isn't silly. Not crazy about Ronnie or Roni though.
I prefer Veronica to Heather. Heather had a very short shelf life as names go; it was the Brittany of its time. I knew loads of Heathers growing up. There is a good reason why the movie was called Heathers rather than Mindys or Pams or Berthas; Heather was very much coming into fashion at the time the Heathers wwould have been born, so it makes sense.