Fairly easy, as for best one I am big on OVO.
Customer Service super good, and you get a pretty good deal if you don't mind submitting readings monthly but if you have a smart meter even better. And I feel like I am striking a blow not using one of the big six.
I was with Ovo for 3 years, excellent company and customer service and pretty much the cheapest for me throughout that period. Last two years they've been over £200 p/a more expensive than SSE and Sainsburys/BG - just too many beer tokens to ignore....