I've gone with Ecotricity for the moment. I like the company, like what they stand for and they are very user friendly for meter readings, bills etc. Not sure whether they are the cheapest though.
all in it for one thing , making money out of the customer/ POOR CUSTOMER SERVICE , some more than others ,depends on how you use your energy
regards
DR
Another vote for OVO. Never had a problem with them in the 4 years since I switched from British Gas. They pay me interest on any money I am in credit with them. British was in comparison are the most useless company I have ever had the pleasure of dealing with. Quite frankly why anyone still uses them is beyond me. Wish I'd switched earlier.