CommentTribe
Follow the people in the comments, not just the channels.
CommentTribe is a free browser extension for Chrome and Firefox. Star the YouTube commenters you like, and it spots them on every video you watch.
Spot your people
Starred commenters are highlighted and pinned near the top, and a "who's here" banner lists them on each video.
Keep up with their channels
See each person's latest upload and stream, and get a notification when a favourite posts.
Read the comment section
A word cloud of what people are saying, every timestamp in one list, and a search for any word or name.
Built for communities
Group people into communities like Minecraft SMP servers, and see each person's Minecraft skin.
Your data stays with you
CommentTribe has no accounts and keeps everything in your browser. It works without any setup. For deeper scans you can add your own free YouTube API key, and the extension can make one for you: sign in with Google once, and it creates the key in your own Google Cloud account. Read exactly what it does in the privacy policy.