Hey Jetjockey,
Well the great thing is that your test soaking in all the spas which is really important! Now it comes to breaking them down and finding the differences between them all, and I'm here to help! I know hot tubs in and out and can give you the pros and cons on each.
1. Marquis Epic- Great spa wonderful company/downfall they have bypass filtration and cleaning cycles.
2. Sundance-have the same issues as Marquis
3. Hot Springs-downfall they are pricey but thats really it, they have no bypass filtration, no cleaning cycles and a great warrenty. The tub cleans 24hrs a day silently!
What does By-Pass mean to you?-It means that when the jets are on, the tub has intakes that suck in the water and passes the filter and comes straight out the jets. So this being said, if you have a hot tub party and have a bunch of people in there and the water gets gross, when you have a system with bypasses the water isn't being filtered its just mixing around.
Cleaning Cycles-now mostly all tubs have them, and the tubs you are looking at have great insulation so noise shouldn't be an issue. But the down fall to having a tub with cleaning cycles is that the water in the tub will sit there stagment for a few hours until the cycle turns on and then its being pushed through the filter compartment.
Hope this helps you! Best wishes and happy soaking!
~~Hottublady~~