From Shimano, the best looking for me is Dura Ace 7700. Dura Ace 7400 was also nice, but 7800 had hideous those bulbous cranks, and everything after that is an abomination of asymmetry and cheap finishes. Because of their painted finishes, all Shimano groupsets look the same now.
Campagnolo C Record was their pinnacle, but I love the angular Victory chainset, and monoplanar brakes have a beauty.
I also love the industrial looks of the Mavic rear derailleurs, and the Simplex/Mavic SSC downtube shifters are magnificent.