I have switched multiple accounts from ESB to Airtricity to Bord Gais. Its a very simple process and easy to do, you are buying 'virtual' electricity so there is no physical changes required.
However the Airtricity billing system is shockingly bad, they insist on monthly billing which is a pain and if you submit a reading they put it on the bill but don't use it to calculate the cost, they stick with their estimate (bills are read 4times per year by ESB networks). So even though they say send us your reading, the bill won't be based on it. I gave up cos I wanted really accurate bills and they couldn't/wouldn't oblige.
Recently I've moved to Bord Gais (business only I think) and its very good and two monthly billing which suits me best. In my books anybody but ESB is best, they've screwed & polluted the country for long enough.