In reading this thread, I realized I need to play Dunfanaghy and Narin and Portnoo to have a more complete experience with courses in Donegal. Given that I have so much experience playing Ballyliffin, I will add some comments.
From my perspective, Glashedy and The Old Links tend to have stretches of holes that are runs of very good holes and it is hard for me to think of one as particularly better than another, since they can vary so much from day to day, due to wind and weather, but that is Donegal and most of the island of Ireland.
The opening three holes on Glashedy run up to and then into massive duneland. I am hard pressed to pick one as my favorite of the three, but they are three really solid holes to start the front nine. On the back nine, 12, 13, and 15 constitute another stretch of demanding holes. Holes 12 and 15 are long par fours that are dog leg holes that run in opposite directions with the 15th green located in the area around the 12th tee. Number 17 is an excellent long par five and the finishing hole runs through some smaller dunes back toward the club house.
On the Old Links, the fifth hole, an uphill par three is probably the most memorable due to the location of the green in a flat area between the top of two peaks of a larger dune. Anything short runs to the bottom of a steep slope. There is forgiveness long. I am partial to the second hole, due to the length and the rumpled fairways, extending until the fairway slopes upward to the green. The third hole is a shorter par four with penal fairway bunkering, with sloped and rumpled fairways. The stretch of holes on the back nine among my favorites are 13, 14, 15, and 16. Number 13 is a bit away from Pollan Bay but 14, 15, and 16 run along the water. I don't have a favorite among these to suggest, but I look forward on each round there to playing these holes.
At Rosapenna Old Tom Morris, I concur about #13 and 14, the short par four and the subsequent par three as being among my favorites. On the Sandy Hills course, my favorites are #4, 6, 10, and 12, mostly due to the massive dunes that are part of the visual character of the holes.
Agree about #8 at Murvagh being an amazingly difficult par five. I also like the finishing hole there.
I ordinarily stay near Ballyliffin for three to four weeks. This May and early June I will be there but the Glashedy course will close for the Irish Open a month before the July Irish Open. I will probably return to some of my old favorites and play a couple of other courses in Donegal I have not played before. An earlier thread discussed venturing into raw playing environments. It can get pretty raw in some parts of Donegal and even the better courses have a raw quality to them.
Charles Lund