The Bulma CSS framework, does in my experience produce a lot more fluent and robust responsive behavior, with much less code, than Bootstrap.

What is more important, is that it allows a reasonable development cycle by hand, after the design is exported. This is paramount to my workflow since I typically have to export the design to adapt to CMSes such as Processwire, Drupal etc, making it very hard to go back and use webflow for further modifications.