I like how minimal Bootstrap 4 is. I also like the SCSS core itself. It's very well written and I learned a lot from reading it. I worked with Foundation 5 + 6

I like how minimal Bootstrap 4 is. I also like the SCSS core itself. It's very well written and I learned a lot from reading it. I worked with Foundation 5 + 6, Semantic UI, Spectre, Bulma and Bootstrap 2 + 3 (and some more lesser known Frameworks) and I must say that the Bootstrap 4 team really nailed it. All the other frameworks are good, but this is just great to work with.