Well, I've had a Monaco diesel and a 2005 Revolution LE. In my humble biased opinion, I would take the Revolution hands down. Although it may have laminated walls, if you look into the details of the construction and the way things are assembled and connected, you'll soon see that the Revolution LE is the better of the two. In addition I like the side radiator of the Revolution vs. the rear radiator.
There is always this back and forth about the Roadmaster chassis vs. a Spartan chassis. They definitely ride and handle differently. Drive one and see which YOU prefer. My preference is for the Spartan. I found the Roadmaster to be a little harsh for my taste. In addition it has considerably more unsprung weight which tends to add to its harshness. As a side note, it is interesting that the new 2015 Dynasty is being built on the "new Roadmaster chassis" which is identical to the Fleetwood Liberty chassis.
I would not worry about the engine choice. I always said I would not choose the coach by the color of the engine. I had had 3 Cummins engines before the CAT in the Revolution. Personally I couldn't see much difference. The C9 is a very good engine. We drove ours over 95,000 miles before trading it on a new coach this spring and it did VERY well for us.
As others have said, drive one, think about living in one, and pick the one that fits you best!
Good luck!
Ed