I had this problem a few months ago! Me and my bf planned to move in together, found a house etc etc, so before we moved in we tried to get some quotes but it is so difficult!! They wanna know how much electricity and gas you are gonna use averagely and we had no idea!! We are going to get our first bill through in December.
Were with NPower at minute but after this bill I think I'm going to switch cos we will have an idea of what we are using (even though you use more in winter).
We haven't set up a direct debit either in case we get charged too much (they tried to charge us based on the last occupants usage!! which was a woman, and 2 kids) Me and my partner both work and I'm also at Uni, I'm hardly in the house and he's only in at night, so we don't use that much.
My Uni friends who have been with British gas a few years now say they found them the best if you can get on the right tariff!