I'd agree with Gladman. It's very difficult to separate three from the others. So, I've chosen the ones that I'd take someone to see if they were around with me, in the order that I'd take them. Each offers something unusual. I love them all.

1. Bohonagh (Stone Circle and Boulder Burial)

http://www.themodernantiquarian.com/site/1027/bohonagh.html

2. Ballyroe (Boulder Burials)

http://www.themodernantiquarian.com/site/12822/ballyroe.html

3. Last minute change of mind from Maulatanvally (Anomalous Stone Group) to Lettergorman South (Stone Circle)

http://www.themodernantiquarian.com/site/3699/lettergorman_south.html

Even though I'm sure of it and sure of my reasons for selecting it, the chance must remain that it is not prehistoric. It is, after all, anomalous.
By including Lettergorman I keep the quartz - and a sly view across the valley to the former - but add a Winter Solstice alignment to the Equinox orientation at Bohonagh. And it's great.

Sorted.