We are on EE, not out of active choice, but we have simply been migrated across over the years from Freeserve, over Wanadoo, to Orange, and then to EE.
As most lines in our area are Exchange Only (EO), I do not think there is too much difference in the speed you will achieve on a cobber line with any provider.
The best we have managed is around 1.6Mbps, but we are currently getting approx. 0.3 to 0.5Mbps, reminiscent of a dial-up connection of the olden days.
However, a lot depends on your individual set-up, so perhaps you will do better. Some people seem to have have achieved 2-3Mbps or more with various providers, or you may want to consider joining the current Hyperoptic initiative – please see: http://www.rainbowquay.co.uk/Forum/index.php?topic=300.0
It is likely to be years rather than months before we get fibre optic in our area, and I personally find this interactive map useful for an overview of the current status: http://maps.thinkbroadband.com/#!lat=51.49608142830186&lng=-0.03656346429443147&zoom=15&type=terrain&speed-cluster¬spot
I hope this helps.
10, 2 RQ