Im not sure that any are necessarily better, 1mb broadband is 1mb broadband, all suppliers have their pros and cons so see the BB sticky for where to get info on each. I will say if you can get eircom you can get BT as its cheaper. 40e per month for phone and line inc rental.
Then get yourself a wireless router for the incoming BB line and 2 USB keys so youre not relying on having at least 1 pc connected to the router. See the usual tech vendors (elara.ie, marxcomputers.com, peats, maplin, komplett, pcsmart, pcworld, argos) for offers on routers and USB keys. You should get set up for less then 100e if you shop around. Theyre all much the same.