My gf and I took 2 day tours: Cliffs of Moher and Giant's Causeway.
The Cliffs of Moher tour was OK. Some stops had too much time and the driver ended up cutting off the last stop at a castle altogether. The lunch break was terrible. Around 3 tour buses at the small Doolin town filled up the restaurants which clearly did not have enough capacity. Result: a hurried up overexpensive lunch with no place to sit.
On the other hand, the giant's cause way tour was nice. The trip to Northern Ireland was cool and worth it. However, again, there were stops that were not worth it and this took time away from those which were actually cool. 15 mins at the Dark Hedges is only enough to walk to the very entrance and take 1 pic before having to run back to the bus to not be left behind.
Also, the driver waited around 45 mins for some people that were late in Belfast, therefore all the tour went out of schedule (very bad for those who woke up very early and on time)More