Change of subject - any thoughts on the difference between user-friendly URLs?

Root paths route to usernames:

- https://twitter.com/username

- https://github.com/username

- https://www.instagram.com/username

Sigil-scoped paths for usernames (these also use www-prefix):

- https://www.threads.net/@username

- https://www.youtube.com/@username

Path-scoped usernames:

- https://www.reddit.com/user/username

- https://www.reddit.com/u/username (redirect)

- https://bsky.app/profile/username.bsky.social

There's obviously an engineering cost to having usernames at the root, but does that make sharing easier?

Which would you use if you were starting a new app?

Is the first option strictly better for growth? Are the technical caveats not worth it?