i just use twitter in Safari. I never liked the idea of a dedicated app for something so basic. The official twitter app does have a cool right click on selected text to tweet feature though.
I have become quite found of Hootsuite-mostly because it is one of the few social media apps that works with Linkedin (or at least one of the better apps that works with Linkedin)
If you have just one account, the Twitter app or Echofone are both nice. If you want to manage multiple social feeds Tweetdeck or Seesmic are nice and have Chrome apps so you can use them in browser and not install locally.
I've noticed there are a number of "best twitter app" type threads but no polls to provide a quick summary of opinions since an outdated one in May 2009. Please consider voting on the poll I've just setup so that it becomes useful (i.e. based on a significant number of votes): https://forums.macrumors.com/threads/1256322/