46A all the way. Hands down. Not only are they far more frequent but there are other buses operating along the Stillorgan Rd that you can take as well. The 19/19a also serves the Glasnevin/Ballymun Road/Ballygall area, and it it is being abolished in July, with the 11/11a route being expected to take up the slack. So expect lots of uncertainty and messing going on there. Stillorgan also has a LUAS stop, that you could use in the event of a bus strike, heavy snow fall, traffic accident etc etc