Neither, they both have pros and cons.
Copilot is great if you are working with Microsoft 365/Word and all that stuff. I like how it knows the email conversations you are having so that it has some context when you ask it questions. I think it is a friendly way for people to start becoming comfortable with AI.
ChatGPT is good if you don’t use Microsoft tools and/or don’t mind that it is a little less pretty. I see ugly things all the time so it doesn’t matter to me. Its cheaper at $20 than $30 for business use, even if it doesn’t have quite all of the functionality of Copilot and the user interface.
Often when you work for a company you don’t have a choice. They tell you not to share data pubically so that means you can’t use things like ChatGPT. Which is fair. They have a right to safeguard their IP.
They both have tons of add-ins, or agents if you want to get technical. They both can connect to third-party services. They both have failures in how they work, and success in how they are good at niche tasks. It really is impossible to give a general suggestion without knowing your willingness to try things. ChatGPT might give you more flexibility, but Copilot might save you time at work. I think both have their place.
Do I like Copilot the more I use it? No. I respect what it is, but it hasn’t shown me it can do things that ChatGPT can’t do. Yes it does have more office tie-ins and functionality, but for me that is less important personally.Your mileage may vary.