I have to agree with the other posters, Material-UI is a little more powerful than Bootstrap, along with providing a more modern feel out of the box, better customization with their theming system. Whenever I used Bootstrap or associated React component libraries, 9 times out of 10 I found myself just using the css classes because the component libraries were quirky and sometimes difficult to work with. Material-UI feels and works better with the concept of composing an application with a variety of components. The docs aren't as easy to use as Bootstrap's but, overall, you will be better served learning Material-UI in my opinion. Unfortunately I can't speak on how they compare to Material Kit as I haven't used it yet.