You should aim to buy a Hot Tub with a good base, obviously one that is able to survive the climate and one that will not rot away with exposure to heat, sun and water and, of course, it has to be impervious to any little beasties like wood-boring termites and that kind of thing.
Products from major North American, European and British Australasia such as New Zealand would fit that category.
We often see Hot Tubs that people change after 5/10 years and the better quality models stand out above the others. The cheaper ones made by lesser known brands and perhaps by large conglomerates who have lost the passion (if they ever had it ) for the product show serious signs of wear and tear where as the better brands often have many years life left in them and can be refurbished and resold.
Also a spa should have sound structural insulation and be designed so that the natural rising heat is automatically retained so that most of the heat generated from the pump(s) during routine filtration and that which is used to power the jets is captured in the spa cabinet so that it may passively heat the water and the air which is introduced in to the Spa either via air or water Jets. Undoubtedly a very clever use of a limited resource.
Some systems can be up to 60% more efficient than Hot Tubs that are made using the full foam system. More often than not a full foam spa takes in cold air from outside of the spa through the heat vent and introduces it into the water thereby reducing your water temperature and creating discomfort. The heat generated by the pump is vented to the outside and lost. Avoid full foam spas as they may cost more to operate and repair. It is very difficult to find a leak beneath layers and layers of foam.
Make sure that the Hot Tub you consider uses quality computer controllers with custom built in electronics and automatic built in safety features and economy modes of operation when and if required. It is very useful to be able to have a sleep and economy mode as well as a standard mode. I would take it for granted that any spa has freeze protection built in to the controller so that the heater would spring into action with in a certain temperature range of say 4 degrees c so as to ensure that no damage happens to the SPA.
Balboa a Californian based company is one that makes very good state of the art controls and their service and back up is second to none. Replying to emails in a few minutes and being very accessible on the telephone how many international service companies can fulfill that criteria. The ones that I know I can count on the fingers of my left hand.
The top manufacturers utilize the best controller manufacturers in the world to create custom spa packs and topside controls to complement their spa models. These have built in features that make it so much easier dealing with a spa
These user-friendly intuitive controls take the guesswork out of spa ownership and are designed for a lifetime of use in harsh climates.
Avoid spas with air controls or spas that do not display the hot tub temperature as a digital read out.
Many Hot Tubs are made much more cheaply by using an unbranded and therfore of a lower indeed inferior quality when it comes to the spa electronic pack.
Unknown brand names or bulk imported packs may not stand the test of time and may be very hard to replace if they break down.
The best advice is to buy a proven product from a reputable manufacturer and not a cheap import that way you have proven expertise tested over many years combined with the back up of a Major Western Corporation.