One huge factor is fitting your needs, which is a floor plan, features and and budget consideration. Another big factor is the actual qulaity of materials and workmanship. Finally, condition is hugely important in any used rig and occasionally even a new one. Sometimes they have been damaged in delivery or deteriorated on the sales lot do to neglect.
In can be hard for a newcomer to distinguish between a low-end model that has been dressed up with amenities and a mid-upper grade model that has all those built-in, and often more besides. The comment above about "the same assembly line" is often an important one. A pricy rig that is on the same line as cheaper ones gets the same attention to detail and the same workmanship as the cheap one, and the assemblers have the same time allowance to complete a task before the RV moves on down the line. It is also likely that it is largely the same under the covers. A better choice is the lowest model built on the high end assembly line. It will get the same level of care and underlying components as the top end model. Sometimes it is hard to determine that, though. If the bulk of the manufacturer's models are low-priced ones, chances are everything is low-end under the covers.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL