The 17 series two is better than the series one and in my opinion worth the money the 16 series two is better still.
I had a series 1 and have listened to a series 2. Both are excellent and whilst I did'nt hear them together, I just don't see there is a great difference. I understood that the LS2 came about because of the need to source new capacitors, the old ones being no longer available. Frankly, I think you can't go wrong with either, though an important consideration is that the earlier model seems a lot cheaper 2nd hand.