I like Tweetie. I wrote an article for iphonelife on iphone twitter apps (it not out yet, but here is a short version) and of all the apps I tried, I used tweetie the most when I’m not using twittFilter. (twittFilter is a web app and my fave given that I wrote it). So Gizmodo, which seem to be the site to check now a days, broke a story on tweetie 2 which seems bring a new functionality to twitter iphone apps; offline twitter access. There are some other improvements, but its the offline that sounds interesting. I will wait for a few more reviews and update.
Image from Gizmodo
Here is a clip from gizmodo..
.. The extent of its offline powers alone is impressive: Not only is there caching, but it remembers your exact place in the app, and you can bookmark, follow block or Instapaper while offline. All of it’s ust synced when you go online. ... There’s also drafts manager, live filtering, push notifications (down to the specific user level) and this is killer—the ability to link up people you follow to contacts in your Address Book, plus a dropdown to pick people to @reply…
Tweetie is not in the app store yet, but should be in a week or so. It will go for $2.99 and no free upgrades.