I've been looking for a swim spa. Narrow down my search between Challenger and Endless pool. I would like to test a Michael Phelps signature but my local dealer didn't have one available, so I ended up testing the Challenger. Challenger than the endless pool, nice swim spa, plenty of features. But in my opinion, the endless pool swimming experience will be very hard to match by any other vendor. If swimming is the most important aspect of your swim spa, I would say go with an endless pool.
Good luck with your search.