I am with Ecotricity, and my bills have just come down. They have rationalised their payment schemes and it is now cheaper.
It is easy to change now, and should be done within a month. I never had any problem changing to Ecotricity, and I have lived in four different houses in the last five years. I have a meter reader every three months, and if I think it is wrong, I just ring them up and they change it.
They have a call centre in England, and answer straight away.
I must admit I did a comparison with Ecotricity and First Utility and Ecotricity was more expensive, but I know that my extra payments go to paying for more wind turbines, which I like. They also do research into new energy forms, wave energy and green gas as well as wind turbines.
www.ecotricity.co.uk if you are interested.