I would review Tweetbot for Mac and get into the deepest depths of how good, bad or indifferent it is while comparing it to the mess that is the official client. But instead, just read Macstories’ review, which is about as comprehensive as they get.
The “tl;dr” of the article is that the app does it’s best to ape the iPad experience. Obviously it’s in alpha so some features are missing, or a bit buggy. But overall this is the best experience for Twitter on the Mac.