We're staying in Mahilde the night before a Saturday morning flight from Dublin back to the States. What's the best way to get to the airport from there? I see there are buses, but do they run EARLY Saturday morning? Do you need exact payment for buses, or do you have to have a transit card? Or would a taxi be better?
Since you're likely to be encumbered with luggage then I'd say a taxi is the way to go.
If you have an early start I'd suggest having your host reserve one for you the night before.
Malahide is about a 10-15 minute drive to the airport. I would take a taxi. If you are staying at a hotel, they may have a shuttle service.