My real father died when I was young (around a year or so). The way he died has always left me confused. I feel like he just walked out on us. My step father - whom my mother married a few years after his death - turned out to be a deadbeat. He left eventually.
I remember growing up.. I always knew my real father was dead. Even as a kid, I was smart enough to know that meant he was gone. But I kind of had these fantasies... that I wanted so badly to believe were true... that he was alive and that he'd come back. That he was just on some kind of mission. I hear a lot of kids without fathers (or mothers) do those things. It's hard. Growing up not knowing your father.
However, my mom eventually had a domestic partner. He lived with us for about eight or so years. He was emotionally abusive to us kids, physically abusive to my older sister and younger brother, and physically abusive to my mom. This was, equally, as hard. I think each situation left its scars on me. There is so much anger toward this man, so much anger directed at my father, and so much directed at my step father. I know, logically, I should let go of this anger. But it's hard to do so.
For me, personally, neither is worse. They're both equally hard.
Interesting question, though. I'm sure we'll see various answers here.