Can't go wrong with either of those brands. Both are made by Watkins Manufacturing (who makes Hot Spring Spas). Great customer support, and backed by Masco Corporation (Behr Paints, Delta Faucets, Kraft Maid Cabinets, etc).
As a Hot Spring dealer, I also sell the Tiger River model line. They are a great product. Basically the same spa as a Hot Spring, minus a couple features (no-bypass filtration, ozone, color changing lights). Very efficient, very reliable hot tubs to be sure.
I don't sell the Caldera line, however they are equipped very similar to the Hot Spring line these days, so efficiency and reliability should be darn near the same. If you've heard great things about that particular hot tub dealer, you can't go wrong with Caldera or Tiger River.
Good luck!