preference does not equal quality. Features does not equal quality.
Process Quality is (I used to be a QC tech a while back, and still can often do it better than the engineers), the process of making a product, of consistant build, that meets or exceeds the standards set forth by the customer.
Xmart bikes are rarely quality due to the problems during the assembly phase.
Now material quality is how fit the materials chosen were for the task...at that some Xmart bikes fail miserably. There are some that can fare ok, but those are priced at the same points as bike shop bikes.
When you hit bike shop bikes, you are pretty much assured of quality...it's just what bike fits your needs, budget, and preferences.