Assume that a certain functionality is available in Ruby both as a class method and as an instance method (via a module).

Class method:

require 'foo'  
Foo.foo()  

Instance method (via module):

require 'bar'    
include Bar    
bar()    

Assuming that the two methods behave identically, which would you prefer using, and why?

(Note that the question is not about which to implement, but instead about which to use if both available.)