On grands the materials are mostly the same: Wood, felt and metals.
The components are also mostly the same: lyre assembly, damper tray, lift levers, damper guide rail, damper wires and heads and damper felt.
For the lyre I suppose a solid assembly that donâ€™t give or make noise and pedals have solid friction free motion.
Damper tray assemblies can vary and if itâ€™s not built into the mechanism and Iâ€™m allowed to do the work Iâ€™ll modify it so the lift levers and tray have concentric rotation.
The location of tray return spring should be close to the pitman that lifts it to help avoid warping.
Lift levers can vary and ease of access and regulation is desirable. Some are glued in and the entire tray assembly must be removed to service one bad lever.
Spoons are great for regulation ease but they can cause problems with key end felts because they are small.
Spring as opposed to fixed sostenuto tabs are great.
Symmetry is great with location of guide rail and back action to help minimize excessive or odd bends in the damper wires.
Damper head felt quality can vary - I like the Yamaha CF felt.
I like to put as much felt in the damper heads as possible.
Regulation and ease of regulation is very important.
From the artist perspective the damper kills the sound instantly and efficiently with no buzzing or noise.
Iâ€™m certain others will elaborate much more.