Which PHP framework is closest to Ruby on Rails? CakePHP? CodeIgniter?

I'm going to be switching back and forth between Ruby on Rails projects and some as-of-yet undecided PHP MVC framework projects.

Which of the PHP MVC frameworks out there (CakePHP, CodeIgniter?, others?) is most similar to Ruby on Rails in that the most conventions, locations, workflows, etc are preserved?

I'm looking for the similarity in the way things are done such as directory structures, conventions, etc, not a pros vs cons in speed, extra features, etc.