We see that question all the time, on road bikes and MTBs too. It just isn't that easy. Look for components and frame tubing. That will tell you whether its a good bike. Brands changed model specs every year or two, often for the better, sometimes for the worse. And then they reused the exact model names and numbers, for dramatically different bikes. So an early 1980s Trek 720 was a top of the line touring bike. A decade later, the 720 was a lower end/mid grade hybrid.

And most often, the best finds are the model/brand you haven't heard of. Creating a master list of all the "best" MTBs would be a lot of work, and would most likely be missing a number of models. And who knows what surprise model might show up in your town/C/L?