In terms of memory usage, it's usually Python> Ruby> PHP, which of course leads to Django> Rails> CakePHP. Not just memory, but also tends to hold on to raw performance. EDIT: It's also worth noting that there are, of course, no absolutes. There are many use cases in which Ruby will beat Python, hands down. I think we can all agree that Ruby and Python will always beat PHP, though :)
Here's a straightforward tripartite benchmarking (with Symfony on the PHP side) that states: http://wiki.rubyonrails.com/rails/pages/Framework+Performance. , , , :)
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