Hello. First of all, you're looking at two really good brands. Both well built, and have great warranties. As far as comparisons go, all three models have completely different shell designs (that makes a huge difference to me). I don't know how the pump size works with the Marquis, because the specs say that it's a 110 or 220 volt spa. The Caprio is like that (110/220 convertable), so I'm just assuming that those are similar in power. The Cayman is a 220 only tub, with roughly twice the pump size as the Caprio. The Caprio has a 1.5 continuous hp pump. where the Cayman has a 2.5, which will result in more power to you. I personally like the Caprio shell design better, but the Cayman really has some good power. Again, I don't know what the Marquis offers, this is just my opinion on the Sundance part of your question. Good luck!
