I'll add another element to the discussion regarding Cassique vs. River: Most GCA-types have played plenty of Fazio courses, but a Tom Watson course is a rarer thing...and specifically the "British Isles tribute" factor of Cassique, whether one deems it hokey, derivative or what-have-you, further separates the GC from the River, which while beautiful and tough, is just another example in the Fazio Oeuvre.
I can't speak for anyone else, but my personal reason for preferring Cassique over the River has to do with the unique angles, the burn, the Spectacle Bunkers, the ski-slope-steep approach to the ninth, etc.---it's just very different, and thus appealing.