If you haven't made the big switch yet and dumped the ESB, you are missing out on free money.
There's precious little difference between Bord Gais and Airtricity but they are both miles cheaper than the ESB. For a heavy enough domestic user paying the ESB €500 every two months with quotes from www.bonkers.ie.
Best: Bord Gais (paperless bill with direct debit) €2,623.57
Avoid: ESB €3,000