Always: These are the YouTube channels I'll watch every single time a new video pops up. I prioritize these videos in my subscription feed over all the others, usually because I find the content either super-inspirational or informative. In some cases, it's because I've been watching these YouTubers for a while and I think they're cool and interesting people doing cool and interesting things.
Colleen Ballinger + Colleen Vlogs + Miranda Sings
Also Gus Gus, their cat.
Sometimes: I also really like videos by Anna Akana, PewDiePie, Zoella, Alfie Deyes, Taylor R., Bradley Martyn, Caspar, Laura Lee, Manny Mua, and Alex Wassabi.