BEST HARMLESS/SIGNATURELESS SPEAKERS CAPACITORS.

Clarity CMR, bypass > 5uF with a 0.1 copper film

But I have to ask, a 3 way speaker system is 2x as difficult to make correctly than a 2-way, if this is your first speaker, I strongly recommend:
1 - Visit DIYaudio for help
2 - Learn your taste and build up your skills by making something inexpensive first or

3 - Make a kit

Also, consider a 2.5 way. Smaller, fewer parts, higher efficiency and the bass extension is such that it does really well in a lot of living rooms compared to super speakers.

@erik_squires  Two-way is much easier. Don’t post here much, but I do a lot of DIY speaker building.  The Jantzen Alumen Z are very neutral and pretty reasonable cost for the sound quality they provide.

Hi raul, you helped me pick the Jantzen alumen z's a while back. Have you changed your mind. I think it my be hard to find a boutique cap without a little flavor. Please understand I'm not very experienced with all caps out there only what I have used.  I tried the Jantzen z's in a 2.5 crossover calling for 2 caps in the tweeter section. I ran across a couple used Clarity CMR and bought it for the hell of it to try in same crossover using a combination of CMR and Z's. I really like this combo. I did bypass it with a copper foil Jupiter and Miflex. I did prefer the Miflex so I settled on CMR, Z and Miflex combo. I did use the path resistors with nice results. I have used Duelund as bypass in Preamp as bypass with nice results also but not speakers.Parts Connextion is now having there 25% sale now. Good luck on your search please let us know if you find something better than Z's because I really like that cap.