I'm surprised to hear Ecotricity were more expensive as they've guaranteed to price beat any of the big 6, and have held their prices til the new year, with a genuine promise to try and keep them down as long as possible afterwards.
I'm with them and to me it isn't all about cost. Sure it's an important factor, but I'd rather be with Ecotricity than save £63 quid going elsewhere as they practice what they believe in. Their electricity is 100% 'green' and doesn't use nuclear. Important to some and not others, but they reinvest their money in new generation giving them better control of prices and thus gain more price independence in future.
They also offer a dual fuel discount if you use their gas, which is the greenest in the UK, using a proportion of renewable gas (only 2% but plans to build new plants). Again, you're getting green for less than the big 6.
Finally, they're the ONLY ones actually bothering to offer a free charge network, with plans for many more and offer them free to customers (and even non customers).
To me that dedication warrants some support, by using them as my supplier. Ovo don't bother, SSE don't bother, M&S Energy don't bother, yet Ecotricity do and such support isn't free (even if it is good PR