Both the Caldera and Hot Spot are made in Mexico. They are as close to identical spas as you can have. I sell both brands and I floor the Caldera Vanto / Marino over the Hot Spot Relay / Rhythm. My reasons are I like the in-line sanitation on the Caldera's, I like the look of the cabinet better, and I sell quite a bit of the Midnight Canyon shell which Caldera offers and Hot Spring does not. Manufacturer support will be identical. If they are from different dealers, then look into the dealers reputation.
A Freeflow is in my opinion a huge step downward from what you are looking at. Yes, they are all made by Watkins, but they are not the same spas. Freeflow has a shorter warranty, less powerful pump and less jetting so the performance will be a little underwhelming compared to the Caldera / Hot Spring, and different components. Not to mention being made out of a rotationally molded plastic, which is less expensive and in my opinion not as aesthetically pleasing. The Freeflows should also be about 1/2 the price.