I’d say it’s toss up between Han Solo and Princess Leia. Han Solo’s death was Ben’s test. A test as Snoke says “the deed split your spirit to the bone” then Ben thinks he can’t go back or undo what he has become and what he has done. Then Leia, is a complicated issue. She gets pulled into space but it was clear she wasn’t meant to die. With Carrie Fisher’s passing there was only so much they could do in the Rise of Skywalker. In the Resistance Reborn book, she’s sick and not fully recuperated from the Battle of Oetchi being pulled into space. In The Rise of Skywalker novelization, it clearly states her health is deteriorating and Luke has been telling her to let go and to become one with the force. So when Ben and Rey are dueling her reaching out with the last of her strength to send her love, forgiveness and hope that he’d turn back to the light causing her to die, it makes sense because her final act was redeeming her son. So yeah toss up between Han Solo and Princess Leia for me.

I say either Leia or Han

But I think it would have to be Han

Han solo's death was the only death where i had emotions, the death of the other two didn't make as much sense

I think all their death scenes were handled nicely, so that's a difficult question.

Han - risked (and lost) his life trying to bring back his son. Also the deed that confirmed Kylo's affiliation to the dark side. So, this death has impact on one of the main antagonist's development. It also underlines Han's love for his son.

Luke - sacrificed himself to buy the remaining resistance members some time. I also loved the way his death was done - him projecting himself and eventually taking one last look at the sunset before becoming one with the Force.

Leia - used her remaining energy to talk to her son, trying to save both Ben and Rey.

I don't agree with all of the characters' portrayals in all of the movies but I think the directors did all of them justice regarding how they went down