I use FireFox + uBlock Origin, and never see ads. I did have to disable my other adblock/privacy extensions (DuckDuckGo Privacy Essentials, PrivacyBadger, and Ghostery) for YouTube before its anti-adblock stopped complaining, but FF+uBO seems to work just fine with default filters enabled.
The way I solved this was to leave my regular browser setup alone, make a new Firefox profile just for YouTube, install ONLY ublock origin, and create a shortcut to that profile on my desktop.
Now I only use that profile for YouTube. I haven’t seen one ad since this thing started.