I've seen some people liking and disliking some of the characters, though I think they are all fairly balanced. Obviously, most of them are rather situational, but I figured I'd see what people considered the best and worst overall characters. Here's my opinion:

1. Zlata
Zlata's ability to help depressed survivors better than others is an amazing asset. I've found this incredibly useful. Plus, she has no addictions, knows how to play guitar and has 12 backpack spots. The best character in my opinion.

2. Bruno
His ability is awesome, and one of the most significant ones. He also seems to be rather egoistic, which can be a great thing. The only minus is that he's a smoker.

3. Emilia
This apathetic girl is reliable. She will rarely get sad/content, which allows you to have a reliable survivor. She's a coffee drinker, and only has 10 backpack spots. Despite that, she is still better than many other survivors, in my opinion.

4. Marko
As long as you don't go around killing civilians, Marko is a great scavenger. He is slightly better than Boris, in that he doesn't make as much noise and is slightly faster. Also, he has no addictions.

5. Boris
He's a smoker, and in my experience, get's sad easier than the others. He has a whooping 17 backpack spots though. The fact that he's slow and loud doesn't matter, as long as you don't use him for stealing.

6. Katia
I haven't had much use of her bargaining skills, though they can be useful. She knows how to play the guitar and is a decent replacement for a scavenger.

7. Arica
Her ability is decent, allows you to steal people more easily. She does, however, only have 10 backpack spots which can be a little annoying when you're stealing. She's a smoker, which can be a liability.

Pavle is slightly better than Anton, in my opinion. He is a faster, which can be nice, he can play the guitar and has 12 backpack spots. He is, however, nothing special.

9. Anton
We don't know for sure what Anton's ability does, so that's a minus. He's a rather ethical person, which makes it somewhat easy to make him happy (but also sad). He has no addictions, which is great. I never say no to him if he wants to stay, but there are certainly more favorable characters.

10. Cveta
She's not bad, but not great either. In my experience, she seems to be better with NPCs than other survivors. She's a very ethical person, probably the most, which can easily make her either happy or sad. She has no addictions, but isn't that great of an asset compared to other survivors. I still usually take her in though. In my opinion, she has the most interesting story.

11. Roman
This is just my opinion, but Roman isn't that helpful. He can kill easier, though I very rarely kill people. Plus, he only has 10 backpack spots, so many others will be more favorable to send scavenging than him. He is also a smoker

12. Marin
Marin's ability is great, probably the best of them all. However, the times I've had him, he always seems to get depressed and sick much easier than the others. This makes him a huge liability, and I'd honestly rather spend the extra resources than look after Marin. Marin is also addicted to coffee. He has an interesting story though.