The best one is Tweetbot. Both Mac and iOS (iPhone / iPad) counterparts are the best out there. You don't even need to search.
However, if you're looking for other good option check for Tweetdeck. Despite Twitter said they were discontinuing it the app was updated less than two weeks ago. Because it is an official app, it is free.
Of those three TweetBot is definitely the best. As far as TweetDeck, I thought Twitter said they were discontinuing the regular Twitter app for Mac, not that. TweetDeck is pretty good too though.
Another vote for Tweetbot.
I like TweetDeck--I use it daily!
Thank you All.Who is faster with notifications?
It requires 10.6 or later.can someone please tell me if the official Twitter app is compatible with OS X Leopard? thanks