I'd recommend you seek out Alan's bus on the Blue Route. This route takes you into a wide variety of neighborhoods in the city, giving a great overview. Alan's commentary was well informed and filled with great humor! Loved the trip!
After redeeming your 1- or 2-day ticket, climb aboard a distinctive double-decker bus at one of 28 stops scattered throughout the city. Travel along the red or blue route to tick off top Dublin attractions such as Parnell Square, Trinity College, Christ Church Cathedral, and Dublinia, hopping off whenever you wish to explore further.
On-board audio commentary keeps you in the loop while an open-top upper deck lets you absorb unobstructed views of the city. This tour also includes access to a walking tour and a discount card for numerous Dublin attractions, shops, and restaurants.