CakePHP is built to handle complex websites and heavy workloads and it is ranked in the top 4 most popular on GitHub. It is easy to learn and it also supports MVC model. It is open-sourse and budget friendly.
Fat-Free Framework's documentation is easy to follow making it very easy to pick up. It allows the use to build their own design pattern and it supprts both SQL and non-SQL meaning that you can simply move back and forth but just changing the database settings because your code remain the same.
CodeIgniter offers developers a robust library of code for common tasks. The configuration is minimal making it easy for developers to naviagte.
Many updated features of PHP make the world of development easier and faster to navigate. With the ever changing internet world, these feeatures can make a great deal of difference!