Welcome to our forum.
I have no experience with any of the tubs but there are some people who have Thermo and our moderator has a Dynasty and they like them. I never heard of Spa Crest but that doesn't say much.My advice is to go with what you like and not worry what people may say. Every tub manufacturer has people slinging mud at them, some deserve it and some don't. I don't know what your price range is but for a 3 person tub you have a lot of different options. Many manufacturers can probably be had for about $6000 or less. As far as ozonators, you shouldn't use them indoors unless you have a lot of ventillation, quite honestly you can do without one.
Three person spa? I've got the perfect one for you, the Hot Spring Jetsetter, with DX Moto Massage!! I wouldn't recommend it to you, if I didn't own one myself.
Doc, when is my commision check comming?