Driven in large part by Twitter and other microblogging sites, URL shortening services are growing in number and popularity. This begs the question, is there any advantage to using one over the other?

Royal.Pingdom.com set out to answer that question by rounding up the most popular (and some less popular) URL shortening services and analyzing how much overhead each one adds to accessing the target URL, and how reliable each one is as measured in uptime.

The results are pretty surprising. Of the services tested (Bit.ly, TinyURL, Ow.ly, Is.gd, Su.pr, Sinpurl, Cli.gs, Tr.im, and Twurl), Is.gd ranked fastest with the least amount of overhead at 163ms, with the slowest service, Sinpurl, trailing significantly behind at 847ms. Bit.ly, which dominates the Twitter scene, took the No. 2 spot with 261ms overhead, while TinyURL sat squarely in the middle at 412ms.

But it's the uptime that most people are more likely to be concerned with, especially after the near-meltdown of tr.im, who recently went offline before re-opening and vowing to keep the service alive. Based on Royal.Pingdom.com's 30-day test window, Ow.ly ranked highest with 100 percent uptime, while Bit.ly was not far behind at 99.98 percent uptime. Su.pr, TinyURL, and Is.gd all recorded a 99.9 percent or higher uptime.

Take a peek at the full results here, then hit the jump and tell us which URL shortening service you use most.