I get along better with my father. He was a fun dad when I was a kid (despite having Bipolar Disorder) he would come in my room in the morning once in a while and say, "What are you doing today?" I'd tell him I was going to school and he'd say, "No, you're sick. Let's go to a movie or go downtown to comic book shops." Then he'd call me in sick and we'd go and play.
He's a bit of a nut, a really intelligent guy, college professor (retired) but he's a conspiracy theorist and that can get on my nerves. (He's one who believes 9/11 was caused by the government. I usually try to shut down these discussions before they get started... I really don't believe most of what he espouses when it comes to conspiracy theories and I don't want to get into it with him. He's an old man and I'm not going to argue with him.)
My mother and I also have a strained relationship. She is still bitter about my father divorcing her more than 25 years ago. (Actually, the order was for "mental cruelty" and she had to file it, but he was the one who wanted out.) She got remarried and her husband died, but she's still angry at my father for things that happened, like, 40 years ago. They do get along, though. They usually make an effort on Christmas, and my father always invites her when he has holidays at her house (she always declines) so I have that to be thankful for.
We have Christmas at our house, and I am grateful that they can get along for a while. A few Christmases ago, my mother was really digging into him at Christmas and I had to take her aside a few weeks later and point out what she was doing was childish and hurtful. He NEVER says anything against her, in public or in private and you have to respect that.