I don't think that's even a contest. BNSF hands down. In the spectrum of US Class I railroads, the BNSF is near if not at the top of the list of the best to work for whereas the NS is definitely at the bottom. The NS is widely known to be exceptionally heavy handed in discipline and I hear they don't have guaranteed extra boards. Don't forget they were the only railroad to force their employees defecate in plastic baggies. They haven't earned the nickname Nazi System for nothing.