They were all empty on the inside and hard to root for
Don - Weak A-hole who cheated on his wife, then actually accepts to kill another human being and finally turns out on the person he was willing to go to jail for.
Mona - Such a bitch, really despicable human being, control freak and a murderer. Also willing to kill the only person who is still beside her.
Dusty - Cheating little tramp, willing to ruin a marriage and someone's reputation for a little money (also possibly a drug addict or at least a user).
Murphy - Abusive boyfriend who is willing to pimp out his girlfriend to get some money for blow. Willing to threat, abuse and kill to get what he wants.
It is really a toss who was the worst, although I would maybe go with Mona. But in the end, it was really hard to feel sorry for anyone, despite the fact that all were hilarious at times.