Option B is to get Dublin Bus no. 748 from the airport (every 20 minutes) to Heuston Station, and take the train to Ennis - again you will normally have to change trains in Limerick and generally at Limerick junction too - see for timetables and online booking. Trains are more expensive but generally more comfortable than bus travel.
We will be landing at Dublin Airport but need to travel directly to Ennis. Aside from flying, what is the best mode of transportation to get us to Ennis? How long a trip is it? Can we get a train or a bus at the airport? Any recommendations for a reasonable hotel at Dublin airport with 24 hour shuttle service?