It's fun you ask, because for the first time in many years we have seen quite a interest in the spot price, because it has reached the record high of 0.35usd/kWh (but mostly it stays around 0.12usd/kWh). This has been a record dry automn, combined with very high prices in the UK and Europe (and we export/import power, which affects prices here). You can get all other kind of pricing schemes as well, but as with insurance in general, on average you are going to be best off with spot price if you can stomach the ups and downs.