All new Google Analytics account is set up using ga.js instead of urchin.js now.

The advantages of ga.js comparing to urchin.js is that it is faster, with a smaller source file, automation detection of HTTPS, increased namespace safety, a more convenient set up for tracking e-commerce transactions, more customized code for interactive Ajax-based sites and the ability to take advantage of the most up-to-date tracking functionality as it is added to Google Analytics.

Generally ga.js would be a better option as it has an improved functionality when compared to the old urchin.js file.