Pokemon Stadium 2, hands down. It just had so much more content. You had your standard tournaments and multiplayer battles, sure... but it also had Rental Pokemon for those who hadn't grinded out a team or just wanted to try new Pokemon, minigames for amusing diversions, and even the trainer school for newer players to get educated about strategies and data.
All PBR had was online battling, which was 1) A consequence of superior technology at the time, given at the time of Stadium 2 it wasn't quite a possibility, and 2) Completely ruined by disconnects/rage quitters. PBR had potential, but just... fell short.