Decorator vs Form Object vs Service Object?

1_decorator.rb

class FacebookCommentNotifer
  def initialize(comment)
    @comment = comment
  end

  def save
    @comment.save && post_to_wall
  end

  private

  def post_to_wall
    Facebook.post(title: @comment.title, user: @comment.author)
  end
end

class CommentsController < ApplicatinController
  def create
    @comment = Comment.new(params[:comment])
    if FacebookCommentNotifer.new(@comment).save
      redirect_to blog_path, notice: "Your comment was posted."
    else
      render "new"
    end
  end
end

2_form_object.rb

class CommentForm
  include ActiveModel::Model

  attr_accessor :title, :author

  # validations

  def submit(params)
    return false unless valid?

    comment = create_comment(params)
    post_to_wall(comment)
    true
  end

  private

  def create_comment(params)
    Comment.create(params)
  end

  def post_to_wall(comment)
    Facebook.post(title: comment.title, user: comment.author)
  end
end

class CommentsController < ApplicatinController
  def create
    @comment_form = CommentForm.new
    if @comment_form.submit(params[:comment])
      redirect_to blog_path, notice: "Your comment was posted."
    else
      render "new"
    end
  end
end

3_service_object.rb

class CommentNotifier
  def self.create(params)
    comment = Comment.new(params)
    if comment.save
      Facebook.post(title: comment.title, user: comment.author)
    end

    comment
  end
end

class CommentsController < ApplicatinController
  def create
    @comment = CommentNotifier.create(params[:comment])
    if @comment.persisted?
      redirect_to blog_path, notice: "Your comment was posted."
    else
      render "new"
    end
  end
end