Realistic or Impressionistic

Comparing a Monet to a Rembrandt sometimes doesn't work with flies and fly tying. Some of the best flies are impressionistic and far from the real thing. Having never fished a realistic fly for any amount of time, I am at a loss to really say what works best. Some of the great Catskill tie flies are far from realistic and even thorax and parachute designs are not very realistic!