I don't think it really matters who you switch to, as long as you switch every couple of years or so.
When you switch, choose the lowest cost supplier at the time of the switch.
The electricity and gas supplied will be exactly the same in all cases. There are no such things as Energia electrons, Bord Gaís electrons, etc nor Electric Ireland gas moecules, nor Flowgas gas molecules - by the time they get to your house, it is impossible to say where they came from
If you care about the source of the energy, then by all means choose a supplier with more environmentally friendly sources, but everyone pays for these via the PSO levy so that doesn't really matter either.
Imho, it's mainly a marketing trick to make you think you are doing the right thing. It does have a slight advantage of forcing all suppliers to look for more environmentally friendly sources but that is more a question of regulatory forces than marketing forces.