Dell and gateway are almost identical in all respects - they consider each other their primary competitor, and so keep a constant eye on the practices of the other - parts, suppliers, policies are almost always identical, except at the beginning of a new marketing program of new tech advance. With identical suppliers and parts and both using the Indian tech suport contractors, any difference in experience is pretty much random chance.

Alienware makes game systems - they use the absolute best components, then test thoroughly; that makes them extremely reliable, with top-line components, but the cost of componenents and quality testing gets passed on, so you pay for what you get.

Personally, I assemble my own - much more comfortable choosing my own parts and doing my own testing...