I have been using Twitter now for a while and have found a happy medium for using it. Most of this is due to the Echofon Twitter client. Echofon installs as a Firefox add-on and sits as an icon in your browser. It will post a pop up if you get a tweet and you can click on it to pull up a listing of your twitter feed. Since they have recently released Echonfon 2.0 you can set it to be either a panel, window, or even a side bar. This means a lot to me as it allows me to stay on top of my Twitter, without following another webpage or being annoyed by a bulky Twitter client. Some Twitter clients will make a lot of noise and pop ups, but with Echofon it is very subtle and allows you to check it when it is convenient for you.
Since Echofon installs as a Firefox add-on, this also means that for me I can use this on both Windows and Ubuntu Linux. You would also use the Firefox add-on on a MAC as well, but they do have a MAC based application you can download and install directly, without having to use the Firefox add-on. There is even an Echofon app for the iPhone and iPad, which means I can use Echofon on my iPhone as well. What makes this more appealing to me instead of other Twitter apps, is that it will sync the read list of my Twitter between the iPhone app and the Firefox add-on. That way as I switch between devices, my read Twitter feed is exactly where I left it.
So if you are looking for a good Twitter client, I would highly suggest checking out Echofon. Especially if you are like me and are a Firefox user that has an iPhone, Echofon will definitely meet your needs. And with the recent release of Echofon 2.0 the integration with Firefox 4 is outstanding.