Xpath vs CSS Selectors in Ruby

require 'open-uri'
require 'nokogiri'
require 'benchmark'

url = 'http://stackoverflow.com/questions/8214299/xpath-or-css-parsing-faster-for-nokogiri-on-html-files'
page = Nokogiri::HTML(open(url))


Benchmark.bmbm do |parser|
  parser.report('Xpath') { 1000.times do page.at_xpath('//div[@id="sidebar"]//a[@class="question-hyperlink"]').text end }
  parser.report('CSS')  { 1000.times do page.at_css('#sidebar a.question-hyperlink').text end }
end

another_url = 'https://plus.google.com/+marriott/posts'
another_page = Nokogiri::HTML(open(another_url))

Benchmark.bmbm do |parser|
  parser.report('Xpath') { 1000.times do another_page.at_xpath('//span[@class="K9a"]/a').text end }
  parser.report('CSS') { 1000.times do another_page.at_css('span.K9a a').text end }
end