Gimme - having luggage (unless it really is a huge amount) on the Luas shouldn't be a problem. In reality Luas will leave you nearer the trains in Connolly than any car park, so you will still end up having to lug the bags around a lot.
At least with Luas once you are on the tram you know it will be 30-40 minutes (I think) before you get there, and once you get there you won't have to go looking for parking places, etc . . . you just get off the tram, go upstairs and get your train.
The thing with Dublin traffic is that there really is no fast way, especially at that time of day. Any time I have to go around the city in mid morning I am amazed at the random traffic jams that appear around the place.
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