I've tried Semantic, MUI, and Ant now for 3 separate projects.

The one I gravitate towards now is MUI - it's got the easiest drop in to an existing project, and the most predictability.

Semantic seems to be stuck in a weird place where the main project is barely maintained and a fork (Formantic) is superior, but there's no React version for the fork so you have to make your own React components if you want their new features.

I liked Ant but the integration into existing apps took far more effort than I would've liked. In the end with Ant I gave up and made a fresh project and shifted my existing codebase across.

The only thing I wish MUI had that Semantic was superior in was forms - Semantic has a far better built-in form component, including error/warning/success & loading states out of the box.