I have been with Octopus Energy for several years now.
From my very first interaction with them about switching, they have been excellent to deal with, their staff are extremely efficient, helpful, polite, friendly, and caring.
Also the ability to talk to a human and not some automated robotic answer machine which has a limited amount of useless options, is very pleasing and refreshing these days.
Finally and perhaps most importantly (as I am a pensioner) in these days of austerity and high fuel costs, I have found their tariffs to be both fair and competitive.