Three network will get you unlimited everything and 4G data.
I'd go with them.
I've heard 3 aren't as great as they had been for speeds etcFor £20 a month??I've heard 3 aren't as great as they had been for speeds etc

But unlike 3, Virgin (via EE) is only for 3G data and not 4G?
Decisions, Decisions

Just read the below, looks like there are some issues with slow sim delivery and poor support from Virgin, along with the fact there is a 3.5gb data cap and traffic shaping for high users, £18 for the VIP package does seem good but I'm going to read up more
EDIT: Virgin sim are 3G only at the moment apparently, cheapest EE 4G deal is £21 with a mere 1GB of data allowance, with 4G speeds I'd use that in minutes
http://www.cable.co.uk/guides/virgin-mobile-vip-sim-only/
Today alone I've used 3.4gb on Three.
I rest my case...