Depends on the environment you like to program:

-> if you like non object oriented languages than PHP is the best choise.
Easy to learn and you can use it for web design but also for cli scripts.
(You can define objects in PHP but its not a pure object oriented language)

-> You like more programming in an object oriented environment than Ruby is the best choice.
Ruby is a Very High Level programming language. There are many free books (see Ruby website) and its a pleasure programming Ruby scripts.
If you know basic Ruby, you can start with the framework Ruby on Rails.

Also important is Sun java support -> JRuby (JRuby on Rails) AND Microsoft support -> Ironruby.
Ruby is a much powerfull language than PHP ..