definitely Tough Claws because most physical attacks are contact moves
Tough Claws is better. Perrserker is a Physical attacker, and most of its good moves are contact moves, (e.g. Iron Head, Knock Off, Play Rough, Fake Out, U-Turn, etc.) effectively making Tough Claws better as it boosts a lot of moves, opposed to Steely Spirit's limit to only Steel type moves. Tough Claws boosts by 1.3x, but Steely Spirit boosts by 1.5x. Coverage boosts are also better than STAB boosts because the boosts won't really help if the Pokémon resists your STAB.