It's between Haaland, Lewa and Kane.
Lewa, for all his magical goalscoring numbers, still misses some sitters (like he did in the weekend against Leipzig). His overall game is above the other two, especially is ability to hold the ball under pressure and play key passes to initiate attacks. That being said, he also has the ability to score from any chance (as evidenced by him having a positive goals minus xG stat for the last few years)
Haaland is the more clinical striker but lacks the overall game that Lewandowski and Kane have. Kane is in the middle where I feel he is a better natural finisher than Lewandowski but not as great at off the ball movement to create chances and not as good with his back to goal as Lewandowski.
From his performances, Lewandowski currently holds the crown. But the other two aren't very far behind.