TinyURL was around before Twitter. It’s a useful way to shorten very long URLs, and there are a lot of tools and plugins associated with the service to help out.
However, with Twitter’s 140 character limit and the urge for less text on Facebook status postings, the 23 character TinyURL is a vitrual monstrosity compared to other up-and-coming services, such as Bit.ly, which registers at 19 characters, and the tiniest possible 17 character Is.gd (prounounced “Is Good”) ,Tr.im, and Ow.ly.
Personally, when it comes to Twitter, what is the point of going with anything other than the shortest possible services? One possible reason is that TinyURL is fairly universally known, so people know what they are clicking.
But there are a host of features available for the smaller ones that make them the easy choice of a casual user. Twhirl users may like is.gd because it is built into the services. Tr.im gives users who find a good URL a toolbar shortcut that will shorten the URL and give users the chance to Tweet it then and there. Ow.ly has HootSuite, a Twitter toolbox that lets you manage multiple accounts. All have 301 redirects while Tr.im and Ow.ly offer tools for tracking clicks of your customized URLs.
Right know I’m going with Tr.im because it’s the shortest and has a toolbar shortcut that allows me to Tweet straightaway. But to each his own. There are many other different services not mentioned here.