IMO, the ranking of Hilton in Ireland is:
1. Conrad
2. Hilton Dublin
3. Hilton Dublin Airport
4. Hilton Kilmainham
The best qualities of the Kilmainham are the hotel restaurant is EXCELLENT and pricing/packages can be a good deal, I would almost go so far to say as ranking it #1 in Food Service amongst the others.
I used the Public Transit during my entire IRE stay, and you can go many places, but it's not easy to understand. Getting to this Hilton on public transit was easier than leaving to go back into the city. I used the tourist/day hopper bus for better transport during the day to get places quicker.