I just read a review of five URL shorteners and added a comment recommending the one I'm building my systems on, Adjix.  

Adjix is imho, the best because it automatically stores each link it shortens in an Amazon S3 bucket that I own. If they ever go away, or if for some reason I decide to move on, my links won't break (at least not because of them). I also use a custom domain for my URLs. So I get complete data portability at no cost. Absolutely no lockin.  

I don't own any stock in Adjix, or have any reason to recommend it other than it is a great service.  

I know a lot of people haven't heard of it, but it's really important. Someday a lot of these links are going to break. I'm doing everything I can to be sure that mine last. I know other people care about this. Adjix has made it work.