I'm sure there are differences between the various types of coupling caps and resistors, but at $10/$20/$30 a piece, I'm not in the position to test for the hell of it. (Remember how all those resitors you bought from Angela's add up?) I think this is where the large manufacturers have an advantage. The serious ones set aside time and resource to test and refine beyond what most DIY'ers are able to do in their basement. (Then the accountants come in and tell the engineers to use the cheapest parts.)

Because I can only afford (and allowed by my wife) to build a limited number of amps, I tend to stick to "tried-n-trues"