There was some discussion of these apps on this topic
I used SongbookPro for while. The free version works pretty well for simple songs, but I have my own my own enhanced notation for lead sheets, and was unable to make that work, so I went back to Apple Pages.
IME, trying to create lead sheets on a touch screen keyboard is extremely tedious and error prone. I bought a mouse and keyboard for my iPad, and found that made things a lot easier.