Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
I use TweetDeck & love it... I've been using it for years, even back when I had a Windows machine.
 
I just use Twitter's own client. The only other client I'd even remotely consider is Tweetbot. But, at the price of $20, I just don't see the value in getting it, for a service that is non-essential.
 
Tweetbot, hands down. While it may be expensive, that's all because of how Twitter handles 3rd party tokens.
 
I gave up on Twitter and moved to app.net.

I would rather be the customer rather than the thing for sale.
 
Twitterific, its clean and simple. It synchronizes over all devices so I don't have to scroll back to where I left.
 
Tweetbot. Thought may be expensive but is the best choice for a Twitter Client.

Twitter app is fine, we won't be expecting too much from a free application on the App Store.

Osfoora is also cool. Not as expensive as Tweetbot and has some cool abilities.
 
I use TweetDeck on my laptop and on my iPhone. It's free and very nice (albeit missing some features it used to have… alas).
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.