Another thank you from me. I look into this every year as my bill goes up at a frightening rate and every year I am frustrated by the lack of information. I am currently with nPower and by my maths they still come out the cheapest  however their billing and customer service are horrendous. They calculate their own particular estimated usage and adjust your monthly payments accordingly (in their favour of course!), if you know what you actually use and firmly tell them that you are paying that they don’t argue because they seem quite confused themselves. But it is hard work, sometimes I have to phone through readings several times because some staff don’t know what to do with 3 readings. I don’t even let the meter man in the door because he can only take two readings and this screws the whole system up.
Use them if you dare!
Problem is everyone uses electricity differently so without doing the maths advice is useless. I am all electric so choices are limited however thanks to this website I feel slightly more in control of the situation.