.022uF to .047uF....... The only differences are how soon the tone pot will roll off highs and to what extent. The .047uF will cut highs sooner and a little more overall toward the end of counterclock rotation. Any other theory is bull in my opinion. Polyester film or paper in oil caps will do the job well.:bling:
Some people swear by orange drop caps... I have them, but I honestly haven't ever taken the time to A/B them with any other caps. I prefer .022µF since they just roll off the highs and leave the mids pretty much.