Assuming you're a freelance developer, it really all depends on the project you're working on and the expected final outcomes of the project.
When I first started diving into frameworks the biggest mistakes I made were not understanding the environment I was working in and not taking the time to learn the platforms that were already in place. Unless the client has explicitly told you otherwise or this is a brand new project with nothing to build off of, they'll often want you to build off of the already existing foundation instead of throwing out everything and starting from scratch.
The quickest way to determine which tools you'll need to utilize for any given project depends on the following questions:
If you're unsure of the first two questions, this website is a great resource to get a good idea of the the environment you'll more than likely encounter. The last question can only be answered by the client.
If the client already has a platform that they prefer and want to keep, then it's up to you to learn how the platform operates and its API. If, however, this is a brand new project, a good idea of which platforms are the most popular for their specific task can be found using BuiltWith. It's important to realize that certain platforms and libraries are developed for specific purposes involving certain types of data.
Whichever framework(s) you end up using, just make sure you're using the right framework for the right environment.