24 gauge wire is usually the most ideal trade-off between gauge and flexibility. I've done a number of high-stranded 21 gauge as well which is perfectly fine. I've tried 19 gauge and that's pushing the envelope a bit. I've also done as you mentioned, a completely silver cable using wire from Homegrown, in this case it was someones pair of DT-880s. Since the DT-880s are already high in treble energy, it increased that much more-so with the silver cable in Teflon. The person that I made it for was very happy with it, but my ears being as sensitive as they are, I didn't care for it too much. I'm more of a Cardas copper man myself, but my ears tend to fatigue much more easily that other peoples.
I typically use silver plated copper, as Miguel suggested, or pure Cardas / UP-OCC copper for headphone recables.