After having way too many "custom" classes and hundreds of "custom" functions. I fell in love with CodeIgniter 1.6.3 because of it's MVC. Suddenly my code went from giant blobs of code and HTML to something with structure! I have been using it ever since.
I have tried a number of other frameworks including a few micro frameworks + composer libs etc...
I have learned a lot from messing around with the other frameworks and libraries only to bring what I have learned back into my own CodeIgniter applications. (composer, libraries, ideas, etc...)