I'm leaning toward Sundin.
Tavares was better with NYI than Sundin was for QUE/VAN, but I think Sundin was considerably if not substantially better in TOR. I watched a ton of games of both and he was more fluid and seemed like a better offensive driver and could carry a line better. He had less to work with as well. After Tavares' first season with TOR, it seemed like he stopped being a franchise type centre and became more of a very good net front presence and a guy who was a threat to score goals from the slot area.