There are plenty of great apps for iOS music producers, but there are a few that really stand out. Depending on what features are most important to you, you may have a vastly different opinion of certain apps than another producer. David Israel makes music using iOS exclusively, with a focus on the iPad. Take a look at the article linked below to see if there are any great apps that you've been missing out on.
You can read the full article here: http://smitematter.com/2013/02/02/the-must-have-ios-music-apps-in-my-process/