I recommend to get a fixed price deal then you know price can't increase for term of deal.
Go to http://www.moneysavingexpert.com/utilities/you-switch-gas-electricity and about halfway down are links to also get cashback for switching through them. I went for the £30 cashback from the link to Moneysupermarket (Dual Fuel)
You input your kWh used over last year and deal you're on and it comes up with a table of alternatives and costings.
Did the same last year and got £50 cashback from and also the deal from Power company gave me an additional £105 cashback. This has been paid direct into my bank a/c. Well pleased with that :)
Am just changing again and have got fixed price (before the price increases) and will get £30 cashback from Moneysupermarket.