I would say Pavlik, because Tito VS Hopkins was prime for prime, Hopkins VS Pavlik was prime VS decline (so they thought...)
Tarver is the only non-bum Hopkins beat if you exclude smaller fighters and that ridiculous RJJ rematch. He's a great fighter, but his fans need to realize that his legacy is beating up good, yet smaller guys outside of their natural weight. Tito's the best win out of the small guys, Pavlik is horrible.
hopkins best win by a coountry mile is tarver and thats because of how he jumped up weight to do it before boxing his head off. still, you have to take into account that tarver is a c-level fighter.
People are spending a lot of time attacking Pavlik's skillset here which is ok, but you have to realise that Trinidad did not have great skills either. (I wouldn't even say Trinidad was great, but that's another story.) Trinidad was very limited, relying almost solely on his power to get by weaker opponents who often had little difficulty outboxing him for significant periods before the damage started to stack up. Consider what would happen if Tito fought Pavlik at MW and you might have something of an answer.
Tarver is his best win, he jumped from 160 to 175 and absolutely battered him, almost stopped him. People forget how much of an underdog he was at the time.
Pavlik, because really, at that moment in time, it became evident that Hopkins no longer has the legs to dance and you'd have thought he'd need to dance against a puncher like Pavlik. Plus, Pavlik put a beating on Taylor (at least the first fight) the same Taylor who gave Hopkins a lot of problems.