For $deity's sake don't use the Big Six
I've never seen any of them on the first page of comparison results.
Get your annual totals and plug them into a meerkat, Welsh opera singer, dancing skeleton etc.
Use your real annuals, the standing charge/unit cost variation is very important.
I change supplier every year, and every time I get around 10-15% refunded due to overcharging.
Seems that all the energy companies do the "oh, turns out you do use less than average energy, sorry we charged you too much for six months" - despite providing the annual total use for the previous year and regular meter readings.
I don't think I'm that relatively efficient, everyone uses LED lighting these days.