Susan, most of the common brands are "proven," one way or another. But you must keep in mind that although Beaver, Monaco, Newmar and others are commonly thought of as decent brands (some say excellent), the actual "quality" of some brands varies from time to time, with many of those brands having a bad year or range of years, perhaps even more than one bad range, so you'd need a range of years to go with the brand recommendation. And, as I think you're aware, not all used rigs of that specific brand (or even model) will match that quality.
For example most folks here will agree that Beaver is a fairly high end, quality brand, but the Beaver I had (I bought it used), though there was little evidence of it in the showroom, had been poorly maintained and/or abused, as I found out when hydraulics started leaking, onboard air compressor went bad, and a number of other costly things happened over the years I had it. Most of this wasn't apparent while living in it (other than the hydraulic drips), but became apparent on the road after having it for a while (I won't go into details here). Still, there were several things (peeling veneer, for example) that became noticeable after a couple of years. Yet it was a beautiful, elegant rig, comfortable with lots of amenities that I miss in my "lesser" Newmar Ventana, whether it was the solid wood cabinets, the air leveling, the heavy, smoothly operating pocket doors, or the electronic lighting and awning controls.
From what I've read, even a Newell or Prevost (really high end stuff) can and will have problems, new or used. So the best you can really get from a brand/model is the quality of the design and materials, but little about quality of the actual build work or problems you might encounter. And you can, to a large degree, determine this for yourself from the original MSRP for the rig (often available in NADA book or dealer listings), relative to other brands/models for that year. You might also note that that MSRP can often also be indicative of relative maintenance costs.
So perhaps in your desire to hear what are "proven brands*" you could explain what it is that you expect this "recommendation" to provide. To me, branding of RVs is kind of (but not completely) like Chevy, Hundai or Mercedes -- one is higher priced (and higher maintenance costs) with lots of fancy stuff, but the others still can provide a quality experience for the owners.
* Perhaps you've noticed that most of us seem to be reluctant to say a brand is proven is simply because (as we've all alluded to or stated above) too often that expectation has turned out to be a false comfort. The RV world is different from what you've experienced and expected before in other fields.