I understand why evryone is side stepping answering. Someone made a valid point: One would have to justify why they chose each to be a top 10.
All opinions aside, wouldn't the companies that produce the most units be a factor? Certainly if the company made a poor tub, they would not continue to pump out 20-30000 units plus a year.....
That said, from what I understand to be true these companies produce the most units:
1) Watkins (Hot Springs, Caldera, Tiger River etc.)
2) Sundance/Jacuzzi (also Sweetwater etc.)
3) D1 (+@home)
4) MAAX (Coleman, Elite etc)
Not sure how the rest of the top ten goes, but I would give serious consideration to Marquis, Artesian, Beachcomber, Catalina.....
Certainly everything else in this thread is true: dealer, comfort, wet test etc.
My two cents
HotTubMan