The worst one is Apple's. There's a reason why they're so famous for their snobby customer service: they don't need to put in any effort because they know most people are going to throw their hands up and buy a new computer instead of trying to fix whatever issue they have.
But I also can't stand Microsoft's forums, because there's always at least one guy who chimes in with a condescending tone, like he thinks he knows more than you do about your problem. And then there's Google, which doesn't even have a real forum at all—just an unresponsive help page that sends you back and forth between different sections until you give up out of sheer frustration.