This is a pretty good post, matt buchanan put a list of twitter apps for the iphone together with screenshots and grades.  Now I’m using Twinkle myself where before I was using twitterific, but fount twitterific buggy. Matt has Tweetie as the best overall, but eh, I dont know, seems to much kitchen sink to me. I was kinda surprised he gave Twittelator Pro to marks, issue I have it with it are exactly what I do not like about it.  Sorry, when it comes to twitter, its really important that things work; nothing bugs me as much as a slow UI.

Nambu, seems interesting if you use friendfeed and ping.fm  I actually thought the UI was ok, I do not mind it being a bit squished.

The Quicklist
• Best Overall: Tweetie
• Best Paid: Tweetie
• Best Free: Twitterfon
• Most Powerful: Twittelator Pro
• Best Tweet-Only: Tweeter
• Worst Twitter App Ever in the History of Twitter Ever: Tweetion
• Creepiest: Twittervision

.. check out the post, its not complete, but a good place to start if you are new to twitter for the iphone.

iPhone Twitter App Battlemodo