Nobody makes "the best", except in their own estimation. Some good names, in no particular order are, Hotsprings, Jacuzzi, Sundance, Master, Cal, Marquis, Emerald, Beachcomber, Coleman, and the list goes on.
One to avoid would be anything that appears to cheap to be believable. Like some of the stuff sold at big box stores, out of warehouses, or on the internet.
Clue: If you see a spa with a "regular" price of $15,000 being sold out of a garage or warehouse for about $5,000 you're really getting a $5000 spa, not a $15,000 one.
If you've never heard of the brand, and there seems to have no local dealer network, good luck in getting service and support when you need it.
Never buy anything this expensive without actually seeing one at least plugged and running- to get in a try it out is even better.
Stick with a major brand sold by a local dealer with a good reputation, and you'll do fine.