I've been a member at this place for about 8 years. Prior to that, I was a 10-year member at the Summit in Kalispell, so I can speak from personal experience.
Staff is pretty awesome at the WAVE, it is a bit more intimate/resorty (even though they've gone through two or three major expansions since we joined). Equipment, classes, amenities...all top notch. Constant upgrades in all of the above. Extremely clean and well maintained, too!
The WAVE is more family friendly, particularly with the kids pools and water slide. When I was a member at the Summit, the pools would quickly get overcrowded, and there were occasional cleanliness issues, but that was years ago, so it's not fair to judge. Love the WAVE, love the staff and the atmosphere. Ten stars.