"I think they are both great suppliers, but there is a fundamental difference to be aware of if you need to discuss your choice politically.
The argument (fueled mostly by Ecotricity) is that Good Energy encourages and secures only EXISTING renewable sources (although they encourage a climate of investment by paying a premium rate to producers and they directly invest in many small scale generation start ups). The company operates primarily as a distributor of existing green supplies.
Ecotricity argues that existing green supplies would be used anyway on the open grid, and that now other 'brown-tariff' customers have decreased their use of this green supply - thus the net use of renewable energy has remained the same?
But, this argument assumes that only Ecotricity are interested in creating new renewable supplies, and that the premiums offered by schemes like Good Energy's are not sufficient to encourage the necessary growth in the renewables market. If all customers demanded a green tariff from Good Energy (and paid the premium) then we would only have renewable energy (but it would be built and managed by the most efficient third-parties).
Ecotricity invests "all profits" in NEW renewable sources, which they feed back to Ecotricity customers.
Ecotricity is much more aggressive in its pursuit of green power to the masses. They want to move things along faster. It puts less faith in the public to make the switch and therefore doesn't ask them to pay any more. Ecotricity price matches the ordinary electricity tariff in the customers region (not their current deal). However, some [or most?] (the percentage is not advertised) of the energy that standard customers buy is brown (nuclear/coal) and the profits from selling these build new renewable sources for Ecotricity to sell.
I've just seen that Ecotricity has a "New Energy Plus" scheme - it costs around £20 a year more and has the best of both worlds - 100% of profits invested in new renewable sources (owned by Ecotricity), and 100% is green (coming from Ecotricity and other renewable providers) - I wonder if this increases the amount of non-renewable power going to standard Ecotricity customers...
I read both companies blogs, Good Energy is doing a lot of great work for micro generation with ordinary customers (i.e. transition cities, and individuals)
I'm very encouraged by the emerging partnership Good Energy has with the EST, and I will stick with Good Energy because their support for customers generating renewable electricity at home seems more comprehensive at this stage..
If everyone changed to 100% renewable with companies like Good Energy then the problem would be solved. But who is to say that the Ecotricity approach will not work better/faster? Both models should succeed. My only criticism of Ecotricity is that they introduce a lot of distrust into the market and constantly criticise their top competitors. Many confused customers decided the green industry can not be trusted and therefore they do nothing...
Both companies can supply gas - The Ecotricity model sells mostly regular gas and invests in NEW cleaner gas production... http://www.ecotricity.co.uk/
The Good Energy gas model is a bit like the Ecotricity electricity model! they supply regular gas and invest all profits in NEW renewable heat generation in homes