I seem to find an interesting pattern to my personal list of most fun courses: Half of them are designed by MacDonald/Raynor/Langford.
NGLA, Shoreacres, Camargo, Lawsonia, Chicago, Piping Rock, Creek Club, Fox Chapel all are great fun, although most aren't the most difficult courses one encounters. Over in Scotland, my most fun would include TOC, North Berwick, Royal Dornoch, Brora, and Castle Stuart.