Just our experience. We just went through the new or used, gas or DP, etc. We decided that the best way (for us at least) was to shop for a upper level model no matter what the brand. It seemed that the quality used on everything in the coach was longer lasting and better quality.
As for which brands, just go through as many as you can and take notes; otherwise, you will forget important details.
Good luck and happy camping!
Camping with DW over 50 years!
1999 HR Imperial 38WDS, 330hp ISC Cummins
2015 Buick Enclave, AF1 brake system