Well, you should probably visit with a Marathon salesman to get their point of view. Admittedly both Liberty and Marathon are quality machines, and for a used one, perhaps the care and maintenance it has received over it's life is more important than the differences between the brands.

My opinion only, but here is why I like Marathon better:
) From my experience only, and might not apply to ALL Liberty coaches)

1. Gray and Black holding tanks, not a combined unit
2. No dump connection hanging out right in front of the drive wheels where it can get broken
3. No proprietary electronic gizmo that tries to control the generator
4. 6 House batteries, not 3 or 4
5. ALL electric, no propane
6. Glitz is more refined in my taste on the Marathon
7. Dashboard layout on the Liberty with the huge diagram of the bus looks wacky
8. They will give you a wiring diagram if you ask for one.
9. The main thing is that after 7 years of owning the Marathon I have not found one instance of them trying to cut corners on anything, they simply built the best machine they could, cost was not really an issue. Liberty might be the same ( I have not owned one) , but I have been very pleased with Marathon. They also throw in free little parts from time to time, their service is top notch ( and costly), they have a 24 hour help line. They care.