CakePHP, CodeIgniter or Rails for multi-user Tumblr clone?

Definitely Rails. It'd much faster to develop project like this in Rails.

As far as I saw, PHP is lightyears behind from Rails in ORMs. And Rails routing is much better than any PHP framework's as well.

I have been developing in PHP since 2000, and still have a bunch of PHP systems in production (using both CodeIgniter and CakePHP).

I have found Rails to be incredibly more efficient to develop in ... easily 50% more productivity, depending on the use-case. Faster, higher quality. Easy choice for me.

+1 for Rails.

I can't speak about Codeigniter. My general understanding echoes the above statements. Lightweight and no fully object oriented.

I have developed in CakePHP since Jan 2006, after trying to get Rails deployed on my own server and failing badly. Rails was not easy to deploy back then...at least not for me. At the time Cake was the best alternative, and still is in many ways.

Cake is a very competent framework. However, I agree with the statements that it is in many ways far "behind" Rails. Some features are not as well designed, less integrated or simplified in comparison.

A few months ago I spent a couple of day porting one of my Cake apps to Rails2. Just as an exercise. The learning curve was very shallow for someone like me (with a decent grasp of the concepts that Cake and Rails are built on). We recently started porting one of our apps at work to Rails (also from Cake) because we found that support for a lot of things that are important to us are available in Rails or Ruby but not available or as complete in Cake and PHP.

If you are unsure about switching to Ruby you might want to look at Lithium (previously CakePHP v3). It is PHP 5.3 only and still a good way from 1.0 but the community is active and generally it looks like what Cake might have been if it had been started today and not 2005.