When I decided to rewrite my webapp, I considered switching from GWT front end and php backend to an MVC framework. I wanted to try django so I started re-writing my app with it. But I found the learning curve to be too steep and I didn't want to spend the amount of time I was spending learning Python and Django. So I gave up and tried CakePHP, Symphony, CodeIgniter. I found CakePHP and Symphony to be difficult to set up. I may have done something wrong, but eventually when I started with CodeIgniter, everything seemed like a breeze.

So CodeIgniter seems to be the best for me.