I would do the red one, I did this with my family a few years ago when we had guest from The UK
https://citysightseeingdublin.ie/hop-on-hop-off/ They have live commentary, some are the driver talking, some have an separate guide, commentator. One of each passed by this evening as I was waiting for my bus to come home.
The stops are just down the street from Trinity. I would estimate you would get on the bus about 11.30am, which allows for seeing the Book of Kells, shopping in the souvenir shop and then finding your way out of the college to the bus stop.
They have 2 routes
The stops I would recommend on the Red Route (South Side of Dublin) Dame Street Stop
- Either Christchurch Cathedral or St Patrick's Cathedral (both are worth a visit)
- Guinness Store House (if you went in here around 12.30pm you might not have time to do much else as it really needs about 2 hours)
- Kilmainham Gaol (I would visit here over Guinness Store House, its a real 1920's jail, and the exhibition follows the real stories of the leaders of the Irish Upraising against the British occupying army,from the time the prisoners where brought to the jail, to their executions. Its not light hearted or a happy place but its an important part of Irish history)
- Phoenix Park, Dublin Zoo (great place to take kids, one of Dublins most famous and popular parks)
- National Museum - Decorative Arts & History (one of the main Museums in Dublin, another great place for kids)
- Smithfield ( Get off here if you want to visit Jameson Whiskey Distillery)
The stops I would recommend on the Blue Route (North Side of Dublin)Trinity College / Nassau Street Stop
- National Art Gallery (if you are interested in art museums)
- St. Stephen's Green (beautiful city park, great for kids, also this is the the other end of Grafton Street Shopping area)
- Christ Church Cathedral, Dublinia / St.Patrick's cathedral ( see above, they overlap with Red Route)
- Guinness Storehouse ( see above, overlap with Red Route)
- Glasnevin Cemetery (historical cemetery, burial place of Dermot Morgan -Father Ted writer and main actor, Jonathan Swift - author of Guillivers Travels, John Noyd Dunlop -inventor of pneumatic tire and many important people in Irish history)
- Croke Park -home stadium of Irish sport
Out of these lists, I would pick maybe 3 to get off the bus for, given your time frame. You will only have time a full loop of the red route OR the blue route. They both finish on O'Connell Street, the main street of Dublin, on the north side of the river