I snipe and AB
Both are awesome if you put the right data in
I use iSnipe and am quite happy with it, but if I were to start over, I think I'd go with Ballistics AE. One of the episodes of Precision Rifle Podcast had Brian Litz from Berger Bullets on and talked in depth about the development and application of it. Brilliant guy and sounds like a great app.
Isnipe uses Litz's BC's.
And while maybe not his calculations, BC is the most important.