You've finally had enough of your current supplier and have decided to switch suppliers.
I have done it myself many times and I would agree it is the best way to save money.
I have found four different comparison sites:
I'm sure there are a few more out there, but they probably use the same search engines, therefore I'll stick to these.
The good news is that all of them recommend the same tariff as being the cheapest:
Npower's Sign On-Line 14 Paperless Billing
This is good news. Unfortunately SimplySwitch tells me it is actually more expensive than my current tariff. LIES!!!
Simplyswitch, simply have not updated their tariffs for ScottishPower, not very good, not very good at all. I can only presume that they haven't updated the tariffs for Southern Electric either.
Second on my target list, is MoneySuperMarket. They suggest that British Gas Click Energy 6 is almost as cheap as Npower's Sign On-Line 14 Paperless Billing. I can't be too harsh this time, as British Gas Click Energy 6 is a fiendishly complicated tariff, but I make it almost £120 more expensive. They say it is only £20 more expensive. They also get EbiCo wrong, which is an amazing achievement, given that they only have one rate and no standing charge. It seems they don't use Yorkshire rates, but South of Scotland rates which happens to be the highest electricity rate that EbiCo do. This is a bit suspicious, but before I don my tinfoil hat, I enter a postcode in London and they do provide the correct tariff. At any rate they are also out, too many wrong tariffs.
Uswitch and EnergyHelpLine provide pretty much the same information. Incidentally, they quote British Gas Click Energy 6 as £90 more expensive than Sign On-Line 14 Paperless Billing, and happen to get my current tariff wrong. They don't use the Yorkshire tariff for Scottish Power. I know we are in the third world and all that, but do make an effort.
So all in all I have reached the conclusion that you cannot trust neither of the four websites completely. My advice is to do a comparison using either uswitch or energyhelpline and then double check the calculation yourself between the cheapest tariffs. The one thing to bear in mind is that the calculations assume equal energy use throughout the year which is very, very Wrong.
This tends to underestimate the amount of tier 2 gas usage, which results in larger bills. This is because most people tend to use most of their gas during the winter quarter and hardly any during the summer quarter ( I'm guessing none if your cooker is electric).
To give you an idea, I have estimated my usage as follows:
Gas: Winter 47% of total, Spring 24%, Summer 3%, Autumn 26%
Electricity: Winter 29% of total, Spring 23%, Summer 23% and Autumn 25%
This means that on Scottish Power's discounted Dual Fuel Online tariff, the equi-use way of calculating energy costs is £10 more expensive than my more realistic estimate and for British Gas' Click Energy 6, the equi-use way favoured by the sites is £16 more expensive than my more realistic estimate.
As you can see, while it does not vary much it can skew comparisons even further, which unfortunately means that if you are serious about finding out the cheapest tariff you are going to need realistic quarter by quarter estimates of your usage and will need to do the maths yourself.
Finally, while it might run counter to a lot of advice around, it might actually be cheaper to have two different suppliers, even if you forgo the dual fuel discount. For instance while Npower's Sign On-Line 14 Paperless Billing is indeed the cheapest in my case, it does rely on £100+ of discounts that I'll get after being on that tariff for 12 months. This means that I would be stuck with npower for 12 months regardless of any price increases, as changing suppliers before I get the discount will mean losing it completely, which means that I would have been paying quite a bit more than necessary, which brings me to my second best option: electricity from Scottish power on my current tariff and gas from EbiCo. Yes, I won't get a dual fuel discount (£15.25), but gas works out ~£40 cheaper, so I will be ~£25 better off.