I don't have an iPad, but on my iPod Touch I mostly use Stockfish (which is free). It makes a great 'pocket set'. It's easy to set up positions and the engine can help you analyze.
IPad App for analyzing own games

Try shredder and shredder lite (free version). Stockfish "seems" to be a little quicker and sometimes more accurate to me.
For example, I put this mate in 4 problem (From a Bobby Fischer column in Boys Life '66) into both on an iphone 4. The free stockfish app found it immediately and the shredder app only found mate in 5 until I made the stockfish recommended move and then it saw the mate in 4.
I like Chess pro with coach. It has the ability to play variations and also variations on variations. The engine is decent too, although I don't know how it compares to Shredder or Hiarcs.
https://itunes.apple.com/us/app/chess-pro-with-coach/id423198259?mt=8
what's the best app for entering and analyzing your own games on the ipad?