Why have capacitors improved so much over the years?
Not so with all caps
And as far as non-polarized (plastics etc) coupling caps go, the BEST CAP IS NO CAP, if the circuit allows for it to trim out any dc offset manually, or a simple dc servo can be installed. (direct coupled always sound better) but not all circuits can be dc coupled
As for polarized big or small electrolytic power supply caps go, some quality makes NOS (new old stock) can be very good, but very important they need to be "conditioned" first using an ac variac, over a couple of hours and bought up from zero very slowly to their max voltage.
Cheers George