The thing with energy suppliers, is to never trust their estimate of what you monthly payments will be in a quote. Always look at the costs of unit rate price and any standing charges and compare with your current supplier. Also some quotes will include vat and some wont. Then there's different rates that are dependant on how much you use.
You have to do a bit of work yourself with these quotes to get a correct price comparison, the suppliers hope you cant be arsed to work it out, so they can blind you with their often complicated pricing structures.
Ovo, have recently told me about their price rises, so i've dumped them and got a better deal with Coop energy for my leccy. My gas has been with Better Energy for quite a few years now, and even with a recent small price rise, they've still been the cheapest for me to date.