I'd have to have a course that strikes the right balance between quirky fun and challenge. Too much in either direction, and I feel like I would get bored. Maybe that's just my definition of a great course.
Merion, Royal St. George's, Sunningdale Old all come to mind as almost perfect balances.
Elie or Huntercombe would veer to much in the fun direction. Sunningdale New, Winged Foot West, Pine Valley might veer too much in the challenge direction. Over time, they'd just wear me out.