snood,
I agree with cattleskinner, a little rain or snow can be wiped off and no problem with the stainless. If you receiver is blued you will want to keep a closer eye on that as far as oil though. They both are going to have to be cleaned after you shot them, the stainless will buy you a lot more time as far as the elements are concerned though. Stainless will rust from the powders and the salts from your hands so dont ever think you can get away from cleaning it promptly after shooting it.
I have a stainless barrel with the nickel receiver and have never had to worry the whole two week + season. If it gets a little moisture I wipe it down back at the truck and case it. At the end of the season or when I shoot it it gets a thorough cleaning and oiled back down. Never had any problem with rust. You would never be able to get away with that with a blued.
With that said either will serve you well, as far as accuracy mine shoots better than my high dollar muzzleloaders (3 Whites, 2 Knights and 1 T/C) and for a lot le$$.
Good luck with what ever you choose. Let us know what you pick.