Fantastical is the best calendar app for iPhone16 January 2014
It is the easiest to use (for adding/editing events) and the easiest to read (for checking schedules) for most people. Fantastical’s natural language parsing is second to none, making it fast and easy to add events, and it has a simple-yet-powerful design.
I was going to write a review of Fantastical myself, but now I don't have to, since this review on The Sweet Setup says everything I would have said and more. You're doing yourself a disservice if you're not using Fantastical.