We've driven a 2008 Mandalay (a Thor line no longer made, but more-or-less folded into the Tuscany line) for over 3 years, and are still pleased with our choice, having no serious issues. It's a solidly built tag-axle DP, on Freightliner chassis, with Cummins ISL 425 and lots of comfort and convenience -- bath and a half, 3 heat pumps, hydronic furnace/water heater, ceramic tile floors, etc. We actually chose it over a Newmar after driving both, because the Mandalay gave us more features for the $$.
For the most part, I don't buy the notion that a particular manufacturer (with the exception of the high-enders like Newell, Foretravel, or the Prevost-based builders) is "known" for quality or not. Most big RV manufacturers (and Thor is, by most measures, the biggest) make a wide range of products, from entry-level to some degree of luxury. You generally get what you're willing to pay for. That said, some manufacturers have a reputation (deserved or not) that lets them charge more for a similar product. Smart shoppers might steer away from those lines toward one that provides more bang for the buck.
Just my opinion, others will vary ...