Help me compare Ruby on Rails & PHP

I read some articles write " PHP is suitable for small web based
applications, but Ruby on rails is different" and some one say "Because
PHP is open source or low maintainable, it only suitable for medium
project".
I think Ruby on Rails is open soure, is Ruby on Rails suitable for
medium project?
Who can answer this question? Thanks

See how many large sites are running on Rails:

http://rails100.pbwiki.com/Alexa+Rankings

http://rails100.pbwiki.com/Compete+Rankings

In particular look at how many sites are _above_ Twitter in both lists.

How does 250 TBs of data sound?

http://www.vimeo.com/1104164