Monaco used HWH air leveling systems through the 2006 model year. In 2007 they began using the Power Gear Valid air leveling system. Both are great systems.
On the Signature, both HWH and Valid systems were offered with an optional dual leveling system that includes hydraulic jacks in addition to the air bag leveling.
The optional dual leveling is not on my "Must Have" list. If the air only system is in good condition, it works quite well.
I especially like the HWH system. Many of the Newmar owners are taking brand new coaches to the HWH factory to add the HWH Active Air system. This is a $10k smart system with larger air lines, larger solenoids, and a faster computer designed to counteract out of level condition even in emergency lane changes. HWH is advancing the state of the art leveling system.
You can download the original Monaco brochures. These are helpful when searching.
It appears you are making a "Must Have" list for your future purchase. Smart idea. We have looked at hundreds of Signatures/Executives and now know what we like and do not like. I would say a suitable floor plan would be at the top of my list. After that would be my engine choice. Below these are Eaton Vorad Smart Cruise as well as several other options.
Keep asking questions and best of luck with your search.