Ignore comparison sites, they are less than useless. Npower you will be charged hefty hefty heft amounts in winter.
You need to spend a lot of time and a spread sheet and preferably have monthly usage details for each month.
Npower charge you lots of expensive units in the winter, pushing your bills up massively.
It isn't just as simple as 5000 units a x rate and anything above that at y rate. They split that number into different moves.
Iw puke not trust energy comparison sites with a barge poll. They do not take enough info of you, or from the tariff. They also include things like powers £200 cash back. But of course you are then stuck in a deal till you get that back. Because without that cash back they are ridiculously expensive.
I signed unto edf fixed rate as soon as Scottish power announced their price rises, since then most other companies have announced price rises.