H2X Trainer, H2X Challenger, Michael Phelps Signature — which Master Spas swim spa is best for swimming? All Master Spas swim spas create a current of water that allows you to swim in place. The difference is in how the current is produced. And your swim level determines which swim spa is best for you. In this video, Ben and Mari compare swim spa brands. Plus, they show how you can adjust the water current of your swim spa. Use the settings and diverters to find your perfect pace.