For active preamp higher value would be better, but for passive volume control 10k sounds OK. You can get high quality ALPS RK271. You could also use TDK variable attenuator CP2500 (ladder with 20 steps). I believe that both have conductive plastic track. TDK supposed to have a little bit better gain matching, especially at lower volumes. I used ALPS RK271 in small headphone amp I built and matching between channels was perfect. It also felt high quality and robust. Mouser.com sells them but 10k value is less common (zero stock). ALPS Black Beauty would be even better but it is large and was discontinued a long time ago. Get it, if you can find one.
You could also get Danish DACT attenuator (SMD resistor network 24 steps), that has amazing 0.05dB matching but it will cost you over $200. Parts Connexion sells them.
http://www.alps.com/prod/info/E/PDF/Potentiometer/MetalShaft/RK271/RK271.PDF
http://www.tkd-corp.com/products/att/pdf/cp2500as-e.pdf
http://www.mouser.com/ProductDetail/ALPS/RK27112A0-S20-C0-A103/?qs=%2fha2pyFaduju6Dyl2KOrNtbj25hBght...
http://www.dact.com/html/attenuators.html
http://www.partsconnexion.com/product1187.html
http://www.dact.com/html/attenuator_data_sheet.html
I think that DACT recommends 10k for passive pre. I found this:
http://www.dact.com/html/passive_preamp.html
You could also get Danish DACT attenuator (SMD resistor network 24 steps), that has amazing 0.05dB matching but it will cost you over $200. Parts Connexion sells them.
http://www.alps.com/prod/info/E/PDF/Potentiometer/MetalShaft/RK271/RK271.PDF
http://www.tkd-corp.com/products/att/pdf/cp2500as-e.pdf
http://www.mouser.com/ProductDetail/ALPS/RK27112A0-S20-C0-A103/?qs=%2fha2pyFaduju6Dyl2KOrNtbj25hBght...
http://www.dact.com/html/attenuators.html
http://www.partsconnexion.com/product1187.html
http://www.dact.com/html/attenuator_data_sheet.html
I think that DACT recommends 10k for passive pre. I found this:
http://www.dact.com/html/passive_preamp.html