Crossover upgrades: Sonicap? Auricap? Solen?

What are the differences between Sonicap, Auricap and Solen capacitors aside from cost? Is there a noticeable sound difference between them? Are there any other capacitors you recommend?

What about resistors? Are they subject to the same sort of scrutiny?

What about wire? Do you have suggestions in terms of wire type and gauge to use from the crossover to the drivers?

Thanks in advance!
Unfortunately, and fortunately, parts sound different depending on the circut in which they are utilized. DIYaudio is a place to learn more about where and when to upgrade parts.

Paul Speltz's wire is a great place to start (and maybe end) for rewiring speakers.

for the music,