WELL, from what I've learned, stainless.
I have 6 hunting rifles and all have custom stainless rifle barrels now. All have been blue printed, triggers reduced, the whole works.
I spoke with at least 7 custom rifle
builders, barrel makers: Krieger, Hart, Broughton-Richards, Pac-Nor, Shilen, H-S Precision, Gary Schneider, Dan Lilja...about this very topic.
The consesus is stainless. But you will most likely here other opinions that will differ. Naturally. By the way, I'm assuming this is for hunting?
I have owned chrome molly and stainless. I prefer stainless. And for my purposes, will probably never buy a chrome molly barrel unless it is on the factory gun, and if so, it will go straight to my gunsmith for rebarreling anyway. Just my preference.