If it was me, I'd choose Maynooth before Finglas ..... The train from Maynooth will have you into Dublin City Centre in 30 mins. Thats not a long commute. But Gazzer before you buy, take a drive out to the area you are thinking of moving to. Go on a Friday or Saturday evening. Drive around. Park & observe. Are there groups of youths hanging around ? Boy racers ? Are young trees left alone to grow ? Are the houses well painted and the gardens looked after ? All these little things can tell you so much about an area. Good luck.
Be sure to check out potential areas late at night as well to make sure it is both quiet and safe. Having been stuck in traffic in Maynooth a couple of times I can definitely say it's not for me but perhaps you could try the commute a few mornings and evenings to see what you think.