Having used both Ant and Material UI on mid-sized React projects I can say that MUI has much better documentation and flexibility, at a slight cost of having to grok their styling convention. Once you get that it's smooth sailing, with a fairly active community, a lot of intuitive components and generally hassle-free dev experience. Ant was a bit more of a struggle, personally, with less clarity in the docs and a less active (English-speaking at least) community.

I've been working on a large front-end project using Ant and almost used/customized every component it has to offer. One of the best frameworks out there. Everything works great out of the box, and the framework is very well though and designed.

It has components that the rest of the frameworks, including Material UI simply lacks, including a very comprehensive Table component, and a Form component with validation and everything.

I will preface this by saying that we have a bit more work to do to get it working since we are using ClojureScript and Reagent, but we started slowly using antd and replacing our current components. The components look nice (we have used table and select components so far) but the biggest issue has been getting the css to play nice with our existing css