I use Youtube a lot for music listening, but primarily, I like to watch reviews about anything. Even if it's something I've never seen before. My preferred things to watch reviews about though are Pokemon and My Little Pony. Also, I watch a lot of analysis videos, top ten/five countdowns (my favorites are these), and just generally people giving their opinion on stuff. I'm always curious about the opinions of others, and love to watch them.
Most of the things I watch are related to video games or MLP. In fact, I was just about to watch a top five video right now on Pokemon before I found this thread whilst I worked on my commission. On occasion, I'll watch Let's Plays, but I tend to lose interest in them nowadays for some reason. Also, I like anything I can just listen to rather than watch. Because I tend to be working on art when I'm watching Youtube and do it so I don't get distracted whilst working by the fact that I'm not doing anything else. So also, things like voice dramas are awesome too.
Fandubs of video games without voices are among one of the things I watch as well. In fact, I love to see fan projects and fan animations that are well-done in general.
Also, I like to learn new things about video games and media I am interested in, so I'll also watch videos that have those sorts of facts. Sometimes, I'll even watch videos with real world facts!
Things I watch other than that are typically comedy-related. Mostly about Engrish and horrible typoes like Your Grammar Sucks or the LP of Vietnamese Crystal on Delicious Cinnamon. Or readings of horribly written fanfiction/creepy pasta. Any other sort of funny besides that is rare though, because typically, humor on Youtube doesn't amuse me.
One day, I plan on having a channel where I do such things. Analyze, reviews, and opinion-type things. Because I also love to talk about my own opinions. :3