Vodafone and o2 are terrible for data.
EE are just insanely priced, three are great.
Glaucus that Just about sums it up for me.
I've just moved form Vodafone to Three. I've been testing a PAYG EE and Three sim for a couple of weeks and I can't fault Three.
When I called Vodafone to get my PAC code they asked why I wanted to leave and I said I couldn't fault what I was paying each month but there's no point in having a cheap price plan if I can't use it, they couldn't seem to counter argue that so just gave me my PAC code.