The biggest issues with Cat engines comes from Cummins lovers....I am one! Meaning I love Cummins and currently am running a 3126B Cat.
I am pleasantly surprised at the performance of the Cat, and all in all I would not consider it a game changer in decision making.
Used motorhomes Late 90's-2005 era....Look at Foretravel, Country Coach or Monaco. I prefer and over the years have mostly run Monaco Signature and Executive. Am currently driving a Holiday Rambler Endeavor. Much cheaper build then the Signature and Executive but a lot less complicated and has been basically trouble free.