My crossover uses 4 resistors, all in the high-pass circuit (tweeter crossover). Two of them are an attenuation network immediately following the actual crossover components (one cap and one choke since it's a 2d order crossover). I use a Mills 12w wirewound for the series resistor in the attenuation network and a standard Duelund for the shunt.
The high-pass also uses a RC network for some equalization of the compression driver. This network is in series with the driver. I use a Mills in this spot. Lastly there is a Zobel network consisting of a small choke and resistor that is in parallel with the driver. I use a Duelund for the Zobel.
I would not conclude from my experience that series resistors are always more critical than shunt resistors. Both resistors in my attenuation network are very critical. The series resistor might be the most critical, I'm not sure, but they are both very important. The other two resistors in my crossover, one series and one shunt, are less critical sonically.
The high-pass also uses a RC network for some equalization of the compression driver. This network is in series with the driver. I use a Mills in this spot. Lastly there is a Zobel network consisting of a small choke and resistor that is in parallel with the driver. I use a Duelund for the Zobel.
I would not conclude from my experience that series resistors are always more critical than shunt resistors. Both resistors in my attenuation network are very critical. The series resistor might be the most critical, I'm not sure, but they are both very important. The other two resistors in my crossover, one series and one shunt, are less critical sonically.

