Full cashback and great energy deal
I wouldn't advise opting for an energy deal based on cashback unless there is marginal difference in the comparison. I suggest you try a few energy comparisons websites with your previous years readings to gauge a reliable comparison. On this basis, once you find a company your happy with check for cashback (and don't forget to clear any cookies if you do this all in the same day)
In my experience EDF was marginally more expensive than the lowest price on a comparison website I found (a £1 or £2 per month) so I took the gamble on the cash back with Quidco and now I'm very happy with my deal.
Cashback took 6 months and 1 day to be paid, which beats the estimate of 7 months (as currently advertised) so 5* from me.
My DD was actually decreased after initial reading so again, happy chap!
I've had no requirement to speak to EDF, the switch was smooth and I was informed by email each step of the way and they even insulated my loft for free so customer services again, 5*