I played both Portmarnock and The Island last year. Portmarnock is my first recommendation, but I would play The Island again as well. I didn't have any problem booking weekday times. Reserve caddies ahead of time. I think they're well worth it, and makes it a fun experience since we really don't get to do it much here. Here's a pic of our caddies (at Portmarnock) standing on a dune to give us a line to hit.