http://stackoverflow.com/questions/17435426/how-do-i-parse-huge-xml-files-with-ruby-containing-different-tags/17436895

xpath-vs-css.rb

require "nokogiri"
require "benchmark"


doc = Nokogiri.XML <<-XML
  <Listings>
    <Listing>
      <Location>
        <StreetAddress>123 Main St</StreetAddress>
        <UnitNumber>2F</UnitNumber>
        <City>Anytown</City>
        <State>NY</State>
        <Zip>10000</Zip>
      </Location>
    </Listing>
    <property>
      <Location>
        <StreetAddress>321 Main St</StreetAddress>
        <UnitNumber>2F</UnitNumber>
        <City>Anytown</City>
        <State>NY</State>
        <Zip>10000</Zip>
      </Location>
    </property>
  </Listings>
XML


ITERATIONS = 1000


Benchmark.bmbm do |x|

  x.report("xpath") do
    ITERATIONS.times do
      doc.xpath("//*[self::Location or self::property]").map do |item|
        item.xpath("./*[self::StreetAddress or self::AlternativeStreetAddress]").text
      end
    end
  end

  x.report("css") do
    ITERATIONS.times do
      doc.css("Location,property").map do |item|
        item.css("StreetAddress,AlternativeStreetAddress").text
      end
    end
  end

  x.report("find") do
    ITERATIONS.times do
      doc.search("Location", "property").map do |item|
        item.at("StreetAddress", "AlternativeStreetAddress").text
      end
    end
  end

end

% ruby test.rb
Rehearsal -----------------------------------------
xpath   0.340000   0.000000   0.340000 (  0.336482)
css     0.620000   0.000000   0.620000 (  0.621865)
find    0.660000   0.000000   0.660000 (  0.655835)
-------------------------------- total: 1.620000sec

            user     system      total        real
xpath   0.320000   0.000000   0.320000 (  0.321618)
css     0.620000   0.000000   0.620000 (  0.621304)
find    0.650000   0.000000   0.650000 (  0.641275)