British Gas. Been with them for the 40 years of my adult life - since I first had my own place. I find their rates pretty affordable - and I find them (as an energy supplier) to be absolutely. fine. I did switch to Scottish power about 10 years ago. (For one year - just for my electric only.) They tempted me in with a monthly tariff that was a 3rd less that I was on.
Of course, it was an absolute con ... I was using the same amount of electric, so how COULD it be a third less?!!! After a year, I found myself £150 in debt. So the direct debit was bumped up by an extra £14-15 a month to get it to what it should have been - and then another £15 on top of that to recoup the money!
I was conned! So I finished with them, and then I went back to British Gas for electric and gas.
My only problem with British Gas is it's really difficult to get to speak to anybody and get any sense out of them if you've got a problem. I had my electric meter break last year, and I couldn't get anybody out to fix it. They were just insisting they come and put a smart meter in instead. (I do NOT want smart meters!)
I resisted and resisted, and spoke to around 10 different people over a couple of weeks, practically begging them to come fix my electric meter. Every single time I rang - they told me they will only put a smart meter in. When I said 'I DO NOT WANT A SMART METER!' they all said 'WHY don't you want a smart meter?!' Over and over again like a broken record! (Even though I had explained why - over and over and over again - to multiple people.)
It was exhausting explaining myself continually. I never got the same fucking person twice! In the end I put in a massive complaint with Ofgem about their appalling behaviour... They came and fixed my meter within 3 days, and never bothered me about smart meters again!