Conventional wisdom is that stainless is more flame-erosion resistant.
This wisdom started when pre-WWII complaints about the throat erosion of the Win Model 70 .220 Swift were addressed by switching to a stainless barrel. However, extensive star gauging of many barrels indicates that throat erosion will destroy a barrel's accuracy long before bore wear will. Bore wear is due to bullet travel is pretty trivial. I've heard that factory barrel fluting may be unreliable. I've also heard it makes a stronger barrel.