I've got Beer Alchemy and Beer Tools Pro. They are both awesome in their own way, and both have their own unique little annoyances. Can't go wrong either way, in my opinion.
Or you could try Brew Target, which is open source (free). It does about 90% of what the commercials apps do. The main thing it doesn't do is inventory management. I actually think Brew Target's mash designer is more intuitive than either Beer Alchemy or Beer Tools Pro.