Originally Posted by jimc101

There shouldn't be any issue with quality of construction now, frames have to pass EN standards (European standard, but most if not all bikes from CN/TW will conform) so they will all meet a basic standard of construction.

For warranty, this will vary between manufacture and type of bike, and has little relevance to the quality of the frame.

For support, that's not a manufactures job, but the point of sale, as in your LBS, how good will vary from shop to shop.

The MTB market is incredibly diverse which frames being available for lots of different riding types, the intended use will affect geometry, construction features & materials etc; you really need to narrow down what you are looking at to give a more detailed question to get a get a more specific answer.