Tough, If this was who would take right now it would be Hedman without too much hesitation, especially considering contract.
However Hedman took a while to get to where he is, whereas Tavares developed quickly into an elite talent. Performance in early years years be critical, if for example Kane or Toews took as long as Hedman to develop, the Hawks wouldn’t have won their first cup. And it’s not like Hedman is significantly better than Tavares today. Both are amongst the players in the game
Overall though unless I am a team that is already a contender or have a very strong D and gap at C, I would take Hedman. I believe he is ultimately the better franchise player. Based on his style of play he looks like he will have longevity and he was willing to commit to a discount contract longterm with his franchise. Also as of now I believe he is a slightly better player and I like building from the D.