FWIW after years and years of using Bootstrap I'm now using semantic-UI and I feel like it's way ahead. The documentation is weir compared to bootstrap but everything feels better conceived.
I can say I have a positive experience with semantic since I'm only using that now. But I'm very lost and it feels like it could take a long time to learn. Although you can start using it the same as you use bootstrap, include the css and js as CDN and here you go.