I have used JetBlue the last two times flying from Newark. Its either about the same or a bit more than United, but the service is better, there is free DirectTV, free checked bag, and the seats are just so much more comfortable. Leaving Newark they did a pretty good job of leaving on time too. Coming back I get delayed, but I have never been on a flight flying into Newark that was not delayed at least an hour. My worst Orlando to Newark delay (Supposed to leave at 1:30, left at 6:30) was with JetBlue however.
I can't fly Virgin to Orlando, but I flew with them to LA for a business trip and it was just as good as JetBlue with the addition of having wifi.
I flew Spirit out of Atlantic City once and we payed less, but the fees were just everywhere, the seat was designed by someone with scoliosis, and customer service sucked.