My question exactly Maydup !
If BT has upgraded your area to receive its Infinity packages, then you be better staying with them. I changed over to Infinity One and now get about 37 mega pixies, which is marvelous.
I have made the following point many times before but if you can't get a direct link with a fibre-optic cable, as Virgin will give you, you are still going to have your internet service via your telephone line, which only BT can provide.
What is wrong with the service you get from BT now ? If BT hasn't upgraded its green cabinets, you won't be able to get high speeds, no matter who you go with, through your telephone line.