When I have seen this question, I have asked myself ‘better in where?’. Surely BootStrap is the most famous CSS framework in present world. It is famous because it is easy to learn and use. Its great documentation has made it easier to use. That’s why it is the most famous CSS framework.
When you are gonna build a website, BootStrap is a charm. But what about a WebApp? BootStrap is just like a waste of time. BootStrap is less versatile than others. You will like to use Semantic UI in these conditions. SemanticUI is the most versatile framework.
Now-a-days, Google’s material design is the talk of the design community. You may want to implement it for your WebApp. For that you need Materialize.
But if you are sure, you want to use bootstrap but with a different look and style, then try its derivatives: Free themes for Bootstrap