That is a loaded question, as the definition of "best" varies with the user.
Watkins (hot springs, caldera, among others) makes a good, long lasting, and well designed spa. I hate working on them, but can't deny their longevity. They are among my top brands.
But the most important factor in your spa decision is the dealer. A bad dealer will make any spa a bad experience. If you are happy with your Caldera dealer after all this time, you might want to stick with him.
Otherwise, I usually advise that you find reputable dealers in your area and go test out the floor model(s). That can be a problem right now as many dealers have had to sell their display tubs, but is the best way to go about it.
If you want more specifics you need to give some info on what you think makes a good spa? For example, many people want full foam for the insulation value and plumbing support, but others want a spa that is relatively easy to do repairs on so they can fix it themselves if it has problems. 24/7circulation vs timed filtering, ozone, uv, smartchlor, cabinet construction/material, frame material, app controlled, bluetooth stereo (bad idea), etc... Shop brands online for the details and just visit the ones that have what you want. Call the dealers, they will tell you whatever you want to know, in addition to the sales pitch bs.