A practical rough guide:
Long-form writing, analysis, careful reasoning → Claude.
Coding, brainstorming, broad daily utility → ChatGPT.
Anything inside Google Docs / Gmail / Sheets → Gemini.
Anything inside Word / Excel / Outlook / Teams → Copilot.
Image or video understanding → Gemini or ChatGPT.
The bigger insight: most serious professionals end up using two or three. The model matters less than the workflow it plugs into.