I have been on virgin mobile for years, but now also have a couple of vodafone phones - I can say that voda is much better.
signal better, better customer service, better packages - signed up for free texts and free weekends (spend £2.50 for free texts, £5 for free calls during a week), smartstep, passport, mobile tv - great!
I learned more from watching the 2 minute episodes of 24 than the tv show... oh and signed up for that new 'family' package - £5 a month and free calls to 3 other people on vodafone. Excellent stuff. saving a fortune!