Lately and finally, more native true real OS X Twitter Apps have been coming around. So if you are looking to get away from those shitty Adobe Air apps like Seesmic, TweetDeck, Twhirl, Destroy Twitter or anything else. You have come to the right place. :)
There should be no reason why you are using those fake twitter apps especially on OS X. I can understand being use to them before these apps have finally arrived lately or if you are a Windows user using these Adobe Air apps.
Lounge is a great app. I am still using it as my main Twitter app along with Tweetie on the side. I mainly use Tweetie to scroll through my tweets faster as I can use the arrow keys. Lounges offers a great way to save searches and view linked tweets.
Tweetie is now a Mac app and no longer just a iPhone app. This app is probably the most beautiful Twitter app as far as user interface goes to use. Plus it has a great way to pick up where you left off such as what I always missed and from when I used Twitterrific (stopped using, not native and other reasons).
There is also Bluebird and Beak which I have not given too much of a try yet and might at a later date. But I am really liking Lounge and Tweetie right now a lot.