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.