These are two very distinct models offered by D-1. It depends what you are going for. the sarena bay i would say is the more versatile of the two spas. Meaning that you have a lot of room to move about to get the massage you want. Also if you are of average height the bio-form recliners will be a better fit as you shouldn't float out of them. the Ultra-Lounge in the Chairman II is very long, and people 6' and under in height will generally float out of it. The Sarena bay is also very unique in terms of styling when compared with the Chairman II. Both are top notch spas. not to long ago the Chairman II was considered D-1's TOP model, as well as one of the best spas on the market (still is).
Jason,
Store Manager for D-1, Cladera & Nordic Spas Dealer