We will have 9 days in September in Ireland. After arriving in Dublin we would rent a car and drive to Galway and then work our way back and tour Dublin for two days. Should we take the car back to the airport and then a bus to either Trim or Dun Laoghaire and use one of those places for base to tour Dublin. On the third day we have to be airport very early. Which town is easier to airport. I am trying to save 2 day car rental and hassle of returning car before leaving. Thanks so much!
Dun Laoghaire is connected to Dublin by city transportation, Trim is not. Trim is a small town some distance from Dublin. If you stayed in Trim, you would have to take the public bus into the city and back again at night. It is a good idea to get rid of your car before spending your time in the city, but I would stay closer to the city center instead of traveling in. For your last night, if your flight is really early, I would plan to stay somewhere near the airport.
We dropped our car off on the north edge of Dublin and took a taxi into the city center for a 2 night stay, then took a taxi to the airport. It was a Saturday morning and it was very quick to the airport from downtown. Both of the cab fares were very reasonable.