This is strictly an opinion not based on fact or personal knowledge.
I would opt for the Marathon. I believe they are going to be one of the long term survivors, they have a proven product and they support that product.
If I were pressed to make the decision between two apparent equals I would be asking each converter to explain in detail how the systems work and what happens in the failure mode. All coaches are great when everything is working properly, but some system failures on some coaches leave you in a world of hurt. The devil will be in the details.
Also, I would sure as hell weight each coach, each axle, and side to side with full fuel and full water. In my opinion neither are lightweights and front axle overloading would be pretty high on my list of concerns.