Jet-driven vs propeller swim spas: which is better?

There are three common propulsion designs:

• Jet-driven: Several high-pressure nozzles push water down the lane. Least expensive, widely available, and adjustable, but the current is narrower and more turbulent, and air entrained in the stream can feel choppy.
• Propeller-driven: A shrouded propeller moves a large volume of water at lower pressure. The result is a wide, smooth, deep current that feels closest to open water. Common on premium models.
• Paddlewheel: Moves the largest volume of water of the three and produces a very smooth, laminar current. Found on a small number of high-end models.

For resistance exercise, water walking, and casual swimming, jets are genuinely fine. If you are a trained swimmer who will swim laps several times a week, a propeller or paddlewheel system is the upgrade that most owners say they do not regret. Always test-swim before buying — current quality varies widely between models with similar specifications.