Well… Generally when I write Vader, its Vaderkins aka, suitless and
therefor not in pain and more lucid in his thought process. Its also
usually weeks at least from his Fall so he’s not high on the
Darkside anymore either.

And Obi-Wan gives him a reason to reconsider it all, that Obi-Wan
wasn’t the cause of everything bad, that he was trying to keep
Anakin and Padme safe. I honestly logic it from a place of him still
honestly being Anakin, just a bit more unchained and Anakin with the
ones he loves is a gentler sort so that’s why I write Vader the way
he is in most of my fics, that he’s not high on the Darkside and
his own emotional guilt atm, he’s not in utter pain from the suit
and all that happened on Mustafar and he has some vested interest in
Obi-Wan as a person he loves and cares for.

Outside of Obi-Wan, he’s generally not so kind.

So yeah, in a way I guess I do write a kinder Vader but its based on
how I think he would behave if he didn’t have the suit and all
going on.