Steph's, imo. KD is the best player on the team (and he's been a better player than Steph his entire career - Steph had a better regular season last year, but that didn't make him better than KD any more so than it made him better than LeBron), but the offense is built around Steph's offensive gravity and prowess. KD's an offensive mismatch, but Steph is a game breaker. The Warriors become a much more "traditional" (though still ludicrously high-powered) offense without Steph.