Thanks, and keep up the excellent work!
I switch between both still. The key is that notifications come in through Twitter for iPhone so that’s a huge advantage. If I’m just browsing without a notification pulling me in, it’s usually through Tweetbot.
We’ll see what happens with iOS 5 though. Obviously with Twitter built-in, their own client has a huge advantage (and third-party full clients will still be subjected to the OAuth change).