I use Tweetbot (and I am a big fan) to read my twitter stream on the iPad. I've recently started using it on my iPhone. I particularly like the way it synchronises between the two devices (and many other things such as muting).
However I have been surprised by the different reading experience on the two devices. On the iPad one gets to see more of the twitter stream and one is more inclined to follow a link as the iPad is well designed for longer reading.
On the iPhone you get to see less of the twitter stream and while the screen resolution is very good the iPhone isn't really designed for long reads. All as one would expect.
The big surprise to me was the prominence of the tweet pictures in Tweetbot on the iPhone. They are significantly more dominant, as can be seen in my screen shots. Presumably this is a design decision.
As a reader my experience is different. My eye is caught by the picture and I am more inclined to be drawn to read or follow a link. Something to note when composing a tweet. The impact is in the eye of the beholder.