Copilot vs. ChatGPT vs. Gemini: How to Choose the Right AI Assistant for Your Task

Microsoft Copilot, ChatGPT and Google Gemini can all write a decent email, summarise a long document and answer a question in plain English. So the useful question is not which one is "smartest". It is which one fits the place your team already works, and what it can reach once it is there.

We tested that the practical way. We gave Copilot and ChatGPT the same real-world business prompt, word for word, and put the results side by side. This guide shows you what came back, then compares all three assistants on the things that actually decide a purchase: where you use them, whether they can see your work files, and who manages them.

If your organisation runs on Microsoft 365, our instructor-led Copilot training courses are the practical next step after this comparison.

The short answer

• Choose Copilot if your organisation runs on Microsoft 365. It works inside Word, Excel, PowerPoint, Outlook and Teams, and with a Microsoft 365 Copilot licence it can draw on the emails, files and meetings you already have access to.
• Choose ChatGPT if you want one flexible, standalone assistant for writing, brainstorming and code, and you are happy to upload or connect the material it works on.
• Choose Gemini if your organisation runs on Google Workspace. It sits inside Gmail, Docs, Sheets and Meet in the same way Copilot sits inside Microsoft 365.

Most teams do not pick an assistant in a vacuum. They pick the one that matches the software they are already paying for, then learn to use it well.

Same prompt, two assistants: what we found

We wrote one realistic, specific task and pasted it unchanged into each assistant. It is the sort of email an office manager writes every week:

Write an email to our supplier, Northgate Office Supplies, chasing 40 office chairs (order NG-2291) that were due on 22 September and have not arrived. Polite but firm. Ask for a confirmed delivery date by Friday and say we will need to look elsewhere if it slips past 10 October. Sign off as Priya, Office Manager. Keep it under 120 words.

Northgate, Priya and the order number are invented for the test. We ran Copilot through Microsoft Copilot Chat in a Microsoft 365 work account on its default Auto setting (October 2026), and ChatGPT on the free tier without signing in (September 2026).

Copilot returned a subject line ("Follow-up on Order NG-2291 – 40 Office Chairs") and an 86-word email. It picked out the order number, quantity and both dates in bold, which makes the email quick to check before you send it. Underneath it offered two one-click refinements: "Make the tone more assertive" and "Add a request for the delay reason".

ChatGPT also wrote an 86-word email, in an editable panel headed "Overdue delivery – Order NG-2291". Its wording was slightly warmer ("We need these chairs urgently") and it offered to make the email more assertive.

Both drafts hit every instruction: the order number, the quantity, the Friday deadline, the 10 October cut-off, a polite but firm tone, the sign-off and the word limit. Either one could go out after a quick read.

What this tells you: on a well-written prompt, the writing quality is close to interchangeable. The difference between the tools is not the paragraph they produce. It is what surrounds it. Copilot's draft was written inside the same Microsoft 365 work account that holds the user's mailbox, files and Teams meetings. With a Microsoft 365 Copilot licence, the next step (drafting the reply in Outlook, or asking Copilot to find the original order email) stays in one place. ChatGPT's draft has to be copied out into whatever email tool you use.

What about Gemini?

Gemini is built for people signed in to a Google account or Google Workspace. We have not included a Gemini screenshot in this test, so we will not describe a response we did not capture. Google's own documentation covers the setup: Gemini is available as a standalone app and inside Gmail, Docs, Sheets and Meet on Google Workspace business plans, and it works with a free personal Google account too. For a writing task like this one, the deciding factor is the same as with Copilot: whether your team already lives in Google's apps.

The lesson from the test applies to all three. The prompt did more work than the tool. A specific prompt that says who, what, when and in what tone gets a usable answer from any of them; a vague one ("write a chaser email") gets a generic template from all of them. Our beginner's guide to Copilot prompts shows the difference with real before-and-after screenshots.

Copilot vs ChatGPT vs Gemini at a glance

The table compares the three on the questions buyers ask most. Plans and prices change often, so check each vendor's current plan pages before you buy.