Maynooth by a mile I would say; better communications (railway, motorway), education facilities, less low quality housing that will create problems for Swords in years to come. Somewhere I recall hearing of a survey (about four or five years ago) that said that Maynooth was the best place to live in Ireland. Can't remember what it was, but it was quoted buy the local opposition when Thornton's waste disposal tried to build a dump in the posh Moyglare area (they were unsuccessful).
Last time I was in Maynooth I was struck by the way that the town has gained all the modern amenities without losing the esential heart of the high street. They have also a very nice new secondary school under construction beside the university.
Swords has its good points, easy to get to, close to the airport, near the coast, but I wouldn't like to live there. If I were to move, I would certainly look seriously at Maynooth though.