If they play most of the rest of their careers with the Lightning, it will be between Hedman and Kucherov. Going forward, Heddy will age better being a d-man. but Kuch is a little younger. Through 2022 I'd take Kuch for this reason:
2019 he has the highest scoring season post 95/96 (when scoring declined considerably afterwards), then followed that up by becoming the first player not named Wayne Gretzky or Mario Lemieux to score 30 points in consecutive postseasons. Came close again with 27 this year. Ironic that he never won the Conn Smythe, though it did take some otherworldly performances from Heddy and Vasi to overtake him (Point was also ahead of him in 2020). But all in all, this is the highest peak of any player in Bolts history. As Stamkos said when he passed MSL for the franchise points record, he doesn't expect to hold it long.