A lot of people will tell you to steer clear of Master Spa. What kind of support are you going to get from them? A local dealer is very nice to have when a problem arises.
As far as HotSpring goes, we loved our HotSpring Jetsetter so much, we became HotSpring dealers! We've been HotSpring dealers for 1 1/2 years now. HotSpring has been around for 32 years and are a top notch company. HotSpring spas are manufactured by Watkins Manufacturing, which is owned by Masco. Masco produces products such as Kraftmaid Cabinets, Behr Paint and Delta Faucets; pretty good stuff.
What we really liked in HotSpring was the variety of jets, especially the Moto Massage which feels fabulous. The fact that ALL of the water is filtered ALL of the time also helped us pick HotSpring.
Whatever tub you decide on, make sure there is a local dealer to service it for you; and get it in writing! I think some make the mistake of buying a tub, thinking "oh, nothing will ever go wrong with this", as they buy it from someone who won't be able to service it. And then when there is a problem, NOW they're calling a local dealer to bail them out.
There is a lot of good info here at the forum. Enjoy, good luck with your quest, and welcome to the forum!