Which popup will interrupt me next: Cortana, Edge, or OneDrive?

There isn’t a reliable “worst offender”—it depends on what’s enabled on your PC. The standalone Cortana app was retired, so it’s unlikely to be the source on a current Windows setup.

For the other two, the message usually gives it away:

• Edge: website notifications, browser recommendations or default-browser prompts. For website notifications, review Settings > Cookies and site permissions > Notifications in Edge and remove unwanted sites.
• OneDrive: sign-in, storage, backup or sync warnings. Check the OneDrive cloud icon to see whether there’s an actual problem before muting those.

If the message says “Finish setting up your device,” that’s generally a Windows suggestion, not necessarily one of these apps. You can disable it in Windows’ notification settings.

I’d identify the sender on the next notification and disable that specific category first, rather than uninstalling an app that may not be responsible.