Kenny and Lilly are two sides of the same coin in a few ways. And I think, as it stands right now, they are the most broken by their losses.
Andy's actually a pretty good choice too for obvious reasons. I know there's absolutely nothing to back it up but I believe Ben had issues before the apocalypse; what happened just intensified his issues. It's just a gut feeling that I have about him, and it's not like depression/anxiety is massively uncommon in teenagers.
I don't think Clem is broken at all. She has had to acclimate to a different world and has done pretty well for herself. She's perfectly functional and seems emotionally healthy to me, even though she's gullible (which is to be expected for an eight year old).
I wouldn't consider him a contender for "most broken", but I felt bad for Doug in episode 3 because he felt so useless. It was sad hearing that people noticed that he was getting depressed because he couldn't do anything useful. :/
Vernon sort of reminds me of mid-to-late comics Rick in terms of how he views the world. Does that qualify him as broken? Hm. And Jolene was REALLY broken, too, although we didn't really see the events of what made her broken, so it's harder to connect.
And, god, Katjaa...

I miss Kenny's cute family so much. I miss Duck and Katjaa loads. I wish there was more time of them just being cute together.