OK, here's my short list of those that I think give you a quality made spa along with service you can count on: Arctic, Caldera, D1, Hot Spring, Marquis, Jacuzzi and Sundance. They may not be the cheapest spas to buy but IMO they're among the best and whatever you get you're going to want to last you 15+ years whereas a lot of spas made out there end up on Craigslist in half that time.
As far as which to avoid, since you asked I'd avoid Master and Thermospas and I'm not a big fan of Cal. Also, in general I'd avoid the cheap, no insulation, no service spas sold on-line and in big box stores. They cost much more to run (anywhere from $25 to $75 more per month) and end up in the landfill in half the time of a well made spa.
Thanks for the great response. Can you elaborate on what you DON'T like about Master, Thermo and Cal?
One issue I see is that all of these LOOK spectacular on their websites, but I'm sure there are major differences in the long run. I did enjoy the thread on the Costco Lazy Boy spa, and I thought posters on both sides of the argument brought up good points.
Will I be able to afford a spa from the superior lot you mentioned above that can comfortably fit 4 (but ithat has seating for 5-6 people) for under $6500?
ps: Has anyone heard of Saratoga spas (http://www.saratogaspas.com/v3/index.asp) there is a dealer a few hundred feet down the street from me that sells them.