David - I did the same trip last year. You will have a great time. I learned of this site when researching the trip. Many of the courses are profiled here.
Part of our group got there a few days before we got there and said "bring balls" because of the high winds, deep grass and steep golf ball prices.
I would play a second round on any of the courses. My order of preference would be as follows (I attached links in case you don't have them already):
1. Ballybunion Old -
http://www.ballybuniongolfclub.ie/ The old course is pretty hard to get on, we played the Cashen course which gets mixed reviews but was fun to play.
2. Lahinch -
http://www.lahinchgolf.com/I have the fondest memories of Lahinch. They claim to have restored many of the greens to reflect A McKenzie. Others can tell you if they were successful. I can tell you I liked the course.
3. Tralee -
http://www.traleegolfclub.com/indexm.htmThe 2 nines are very different. The front is relatively flat and the back very hilly with some severe shots. On the second hole, the caddie told us to lay up, when we told him we were going to try and cut the corner he said "Aye! We are not here to play pussy golf are we?" I should have listened to him.
4. Waterville -
http://www.watervillehouse.com/pages/frameset_home.cfmThis one was incredibly difficult the day we were there. Very high winds. It is undergoing pretty significant renovation and they are creating a number of additional dunes on the flatter portion of the property and creating new holes.
5. Doonbeg -
http://www.doonbeggolfclub.com/At the time, I did not particulary care for this course. It seemed forced to me, even though it claims to be a very natural course.
We played a small course called Dooks for the second round that day.
http://www.dooks.com/. The course is a bit goofy, particularly the back nine. According to James Finnegan's book, a different member built each of the nine additional holes. It was cheaper than the other courses, is at a beautiful location, has a more authentic feel than others and could be a welcome respite from getting beaten up on the other courses
For your perusal, attached are links to the sites of two other courses we played,
Old Head
http://www.oldheadgolflinks.com/ - fantastic setting, expensive
Dromoland Castle
http://www.dromoland.ie/golf.htm - we played it on the day our flight got in. The castle was memorable, the course mixed. President Bush was about to stay there when we were there so the place was crawling with security.