It's not that simple- it depends on where you live, whether you are an above average or below average user, whether you have Economy 8, whether you pay by DD or quarterly, whether you have a fixed price deal, whether you have a standing charge or a dual rate system , whether you have dual fuel or two separate providers, whether some have put their prices up yet,....
There are comparison sites but these will give different answers depending on what you want and what your circumstances are.
I change every year but it's a pain and I can see why people don't- I can;t persuade my mother and MIL to do it. I have paperless billing but I can see why some don't want it. I pay by DD but my mum refuses to do so and I know some on here won't do it. I use Economy 7 but I do all our washing, ironing, charging up laptops before breakfast which know would drive some people mad.
The energy companies like it to be complicated and know that the majority of people never switch suppliers