I don't really HATE anyone of my companions. But if I'd have to pick one, it would definitely be Boone. Why?
Well, for starters, he's a war criminal. And while my character is by no means peaceful moralist, at least I never executed civilians. Bitter Springs incident, anyone? Suffice to say I used to hate Great Khans, but after hearing their side of the story, I couldn't help but feel sick towards the NCR. Well, Boone was there, knee deep in blood, so to speak.
Second of all, the moment I met him, he just seemed WRONG to me. Maybe it was because of a voice acting, that made him sound like an angsty teenager with a "leave me alone" attitude who tries to talk tough in order to trick the cashier into letting him buy beer. But as soon as I started asking around about his wife, I disliked him even more.
He is a typical guy who somehow finds a hot wife who is dumb enough to follow him to a backwater dump of a town in the middle of nowhere. He also seems to be p***y-whipped, if we're to believe Manny's side of the story, but that's not the point. Anyway, then he is surprised by the fact that she feels miserable all the time, sitting alone in her room all day. I mean, come on, what is there to do in Novac? What the hell did he expect? He can't even take her out for a dinner or something, because the nearest town is few miles away on foot, with angry ants, scorpions and raiders in between. WHAT WAS HE THINKING?!
I'd be surprised if she didn't snap one day and run back to Vegas screaming, after spending one day too many in Novac.
And even then, if you actually take him with you on his little revenge quest, you find out that he *gasp* actually feels BAD about what he did when he was in the army. Good for you, a**hole! Have a cookie! But even worse, he thinks that his wife ending up as a slave, and him being "forced" to kill her somehow ends up being HIS punishment. "You self-centered a**hole! Not EVERYTHING is about you!" you could hear my Courier screaming, if he could scream in the game. In the end, even his wife ends up paying for HIS mistakes.
So all in all, that's what I hated about him the most - he kind of is like an angsty teenager, who just keeps whining and saying it's always somebody else's fault, and everything is always, ALWAYS about him.
I did sympathize with him. I did feel bad for him. But in real life, he's the kind of a person I'd stay the hell away from.
The only other companion I could say I dislike is Cass. Simply because she is a foul-mouthed, immature, impulsive and depressed alcoholic with no more character depth than that. She is useful in a fight, after I give her some decent gear, but that's about it. In real life, I'd stay the hell away from her, regardless of how much I love redheads. Also, her quests are some of the most boring I ever saw in an RPG. A lot of running around from one corner of a map to another, and that's it.
The other companions I mostly liked. Even Lily, who is maybe the most boring character in the game. And Rex, because he is a dawgie.