Whiplash. Might be bias though since it’s my favourite film of modern times. But the editing was sublime, the writing of Fletcher vs Andrew was judiciously done and the message of hard work + unappreciated talent resonated with me.
I haven't watched Whiplash so can't say which is better. Joker is my favourite film of the 2010's though. I'll watch Whiplash sometime in the next few days and then come back to this thread. I'll be astonished if it's better than Joker.