Much of your answer relies on your goals. And, we each have different reasons for using a URL shortener. Most use shorteners by default via some social media tool, to cram long URLs into limited character spaces.

Which URL shortener creates the shortest URL? Creating an unabridged list of URL shortener services is virtually impossible. These are a hand full of free services publicly available.

• http://3.ly/
• http://a.gd/
• http://r.im/
• http://u.nu/
• http://x.vu/
• http://tinyarro.ws/
• http://www.as.vg/
• http://xs.md/
• http://bit.ly/
• http://cli.gs/
• http://lnk.in
• http://pnt.me/
• http://url.ie/
• http://yep.it/
• http://www.fly2.ws/
• http://ne1.net/
• http://nsfw.in/
• http://tiny.cc/
• http://w3t.org/
• http://www.x.se/
• http://yoolink.to/
• http://xaddr.com/
• http://nn.nf/
• http://is.gd/
• http://ow.ly/
• http://tr.im/
• http://su.pr/
• http://totally.awe.sm/
• http://2pl.us/
• http://shrti.com/
• http://www.adjix.com
• http://budurl.com/
• http://snipurl.com/

Limited testing has shown 3.ly to be the smallest URL producer of the bunch. The URL for this article www.tekany.com/content/which-url-shortener-works-best-you and is shortened to 3.ly/NYb by 3.ly. As a short experiment, we created a shortened URL for this article from a hand full of the shorter services.

• http://3.ly/NYb Each time you enter a URL you get a new shortened version, add - to it to see hits
• http://bit.ly/1B3lcW Offers deep personalized tracking and a free personal account (API)
• http://su.pr/2WS4cL Offers personalized metrics, requires an account and uses StumbleUpon wrapper (optional toolbar, API)
• http://r.im/1tee Optional account and tracking and uses wrapper (optional toolbar, API)
• http://u.nu/8hig Add ? to URI to get hit count (API)
• http://x.vu/2230 Offers personalized tags
• http://xs.md/MYV Simple web-based shortener
• http://cli.gs/QhM8jb Optional account and personlized tracking (API)
• http://lnk.in/6u85 Optional account and personlzied tracking as well as password protected links
• http://url.ie/1ybh Optinal post direct to social media
• http://is.gd/1lLJN Simple web based shortener, add a dash "-" to provide a preview version of the link
• http://ow.ly/goRB Simple shortener with wrapper that encourages sharing on other social media sites, connected to HootSuite, a marketing service (optional toolbar with HootSuite, API in the works)
• http://tr.im/qFFm Optional account that allows personalized deep tracking, preferences to create default web browser behavior as well as addons and toolbar browser options

Some URL shortener users do it primarily to track clicks. 3.ly provides a counter by simply adding a dash (-) to the URL. Though that exposes the data to anyone who wants to view it, it is also a plus in that viewing the data doesn't require an account or a log in. Another nice feature of 3.ly is it doesn't provide a wrapper or iframe around the forwarded URL. Though this is often used to promote marketing or sharing, like the su.pr service that encourages people to StumbleUpon your link. Many people just want to see the content and are annoyed by wrappers.

Though most people are just seeking a shorter URL to fit into Twitter, many online marketers and researchers want more data to help them tweak their posts for maximum response. Services like 3.ly are simple, create a small URL and make click counting easy, but don't provide more detailed metrics like where someone clicked on the link, from which social media site, etc. Bit.ly provides data on clicks and the source of those clicks. One Bit.ly URL will tell you if someone clicked on it from Twitter, Facebook, etc. And, you can see retweets, which is an important metric to some.

su.pr provides the additional value of StumbleUpon traffic as well as direct posts to Twitter and Facebook, even scheduling. All sources of traffic and clicks are tracked separately, although the links to include a StumbleUpon wrapper (iframe) which some people do not like. Our tests have shown that StumbleUpon traffic can add measurable exposure to a post.

Some services show the eventual URL by following the redirect and printing the eventual URL. FriendFeed does this in its feeds. But, if you wonder what a short URL leads to, you can use http://untiny.me/ an unshrinking utility to show you the actual URL.

Then there's personalized or vanity URL shorteners. Some of us keep extreme data on traffic, clicks, etc. for market research. The nice thing about roll your own is that the data is all your's. And, you can track others' behavior as well to develop a better understanding of traffic and behavior. bloq.in is a friend's personal shortener running phpurl.