Simon Patten
100+ Head-Fier
I have both. I was delighted with the Gen III but the Pro II is definitely an upgrade. In addition to what the others have said, my feeling was that the Gen III is a warmer, more fun listen, while the Pro II is much more detailed and neutral. I preferred the volume control on the Gen III, it's smaller, easier to use and the battery lasts a couple of hours longer. The Pro II is bigger, has awful button placement, and gets warmer but sounds so much better and you can actually hear a difference between class A and class AB modes. In some ways I miss the Gen III as it made me smile more but I haven't touched it since getting the Pro II.