The therapy is really different between the two. I personally like the Envoy better mainly due to the Moto-Massage but also the fit. I have a hard time not floating out of the Adirondack chair in the Epic.
As someone who is a Hot Spring dealer and was also a Marquis dealer, I feel that Hot Spring is of better quality and better factory support.
If you could be happy with either, then it comes down to the price and your trust in each dealer.