Tweetsville: Is this the daddy of all iPhone Twitter clients?
The most noticeable difference between Tweetsville and its competitiors is that the application sticks to a very conventional user interface: users will be instantly familiar with most of the controls, and a hybrid of both the iPod and Mail-esque look to the application [along with some nice touches that shows you posting tweets as messages 'To the Twitterverse'] mean you'll feel instantly at home.
On top of the nice little touches, there's TwitPic integration for posting photos and linking to them in tweets, a customisable toolbar [and two timeline views to pick from], not to mention built-in support for Twitter Search and Twitter Trends - Twitter's two biggest service additions recently.
Even though there's almost every feature you could need on the go, it's utterly intuitive to use and almost instantly has become my de-facto iPhone Twitter client: sorry Twitterrific.
Some will be unhappy without there being a free version to try - though it's worth remembering the application costs just $3.99, which isn't exactly bank-breaking - and there's no inline @replies to be found in one of the two timeline views. It's also worth pointing out that other clients include features for re-tweeting links. Despite these [admittedly few] pitfalls, for a true Twitter control panel that has almost all the features you need - along with a clean, familiar and above-all thought-out user interface - I can't help but give Tweetsville a very firm thumbs-up.