Short answer: they're more similar than different, but the differences matter depending on what you're doing. Here's an honest breakdown.
The basic situation
Both Claude (made by Anthropic) and ChatGPT (made by OpenAI) are AI assistants built on LLMs. Both are accessed through a chat interface. Both can write, summarise, answer questions, help with code, explain things. At a surface level, they do the same job.
The differences are in how they do it — the personality, the approach, the strengths, and what each one handles better.
What ChatGPT does well
ChatGPT is the one people know. It was first. It has a huge ecosystem — plugins, integrations, a massive user base, and a lot of third-party tools built around it. The GPT-4o model is genuinely excellent, fast, and handles images natively. If you're working with tools that have ChatGPT built in, or if most of the tutorials you find online are written for ChatGPT, that's a real practical reason to use it.
What Claude does well
Claude is where I spend most of my time, and for the work I do — writing, thinking through complex problems, long documents — it's consistently better. It handles nuance more carefully. It's less likely to give you a confident-sounding answer that's actually wrong. It has a very large context window, which means you can give it long, messy inputs and it'll actually work with them rather than losing the thread. And it has a way of engaging with difficult or ambiguous prompts that feels more thoughtful than reflexive.
It also has a personality that, for whatever reason, I find easier to work with. Less eager-to-please, more willing to push back or say it doesn't know.
Which should you use?
For most everyday tasks: either works. Start with whatever you already have access to.
If you're doing a lot of writing, editing, long documents, or anything that requires careful nuance: try Claude. Give it a proper go — at least a week of using it for real work — before you decide.
If you're integrating AI into tools and workflows, or most of the resources you're finding are GPT-based: ChatGPT is fine. The point is to actually use AI, not to optimise which one before you've started.