What is the best / most used one-time character encoding convention in Ruby?

Question

In the Ruby Standard Library, we have a Singleton class:
http://ruby-doc.org/stdlib/libdoc/singleton/rdoc/index.html

We can make any singleton class by including this class inside. I rarely see it being used. When would it be wise to use this Singleton class or just use the simple old class methods - also known as single-user mode methods?

It is said differently: which Singleton coding scheme is the best and why? Here are three ways I could think of:

require 'singleton'
class Foo
  include Singleton
  # method definitions go here...
end

Foo.instance.do_something!

Against

class Foo
  class << self
    # method definitions go here...
  end
end

Foo.do_something!

Against

module Foo
  class << self
    # method definitions go here...
  end
end

Foo.do_something!

Answer 1

WARNING : Opinions Ahead!

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, :

class << (Foo = Object.new)
  # method definitions go here...
end

Foo.do_something!

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Answer 2

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