Madhur Dutta declares Riposte the best App.net client for iPhone on The Sweet Setup:
At first glance, both Felix and Riposte pack quite a punch. But after testing both the apps thoroughly, I believe Riposte definitely has more to offer. It is significanly easier to use (the learning curve for Felix is quite high), it offers some unique features, and it has an interesting pricing strategy. Riposte is free with several “Pro” features as an in-app purchase.
After using Felix for a long time now I still can't figure out how to use it. Swipe up, swipe left, help screens, tap, drag, pop ups, etc. I have the feeling that Felix is onto something with the gesture-based interface but that they just haven't figured it out yet.
After using Riposte for about an hour I immediately purchased the Pro version (you can use it for free and upgrade in the app). Great app. I'm glad Dutta featured it as I simply hadn't ever tried it.