• No ads
• No need to create a Google account
• Tools for managing subscriptions
• Adds ability to listen only to audio
• No need for YouTube app in order to listen to videos on mobile (or use Newpipe on Android)
• No need to "ding" bell, just being subscribed is enough to receive all notifications
• No age-gate
• Dark mode (although YouTube has this now too)
• Free software (AGPL v3 license)

A good Firefox add-on is Privacy Redirect. Apart from handling Youtube can also redirect other services, and it also automatically rotates each redirect from a list of Invidious instances so as to avoid overloading any single one.

See Invidious Instances for a list of publicly available instances.

• "Small acts of resistance are all we need. Together, we make change", Yarmo Mackenbach
• https://reddit.com/r/SideProject/comments/8wvazc/invidous_alternative_frontend_to_youtube/
• https://github.com/omarroth/invidious

Other Youtube front-end alternatives

• yt-dlp
• NewPipe (Android)
• PipePipe (Android), includes SponsorBlock
• yt-local , via reddit thread

Replacing Youtube altogether

Another approach is to replace Youtube with an open-source, federated video host service.
That would be PeerTube (see this blog post by LazyBear).

• https://fedi.video - a good place to get started with PeerTube, by FediThing