If I wasn't already fairly happy with Calvetica ($2.99 in the App Store, recently updated for iOS 7 as well) I'd definitely be taking a look at Fantastical 2 for iPhone ($2.99 in the App Store).
I use Fantastical on the Mac($14.99 in the Mac App Store) and love it's use of natural language for entering events.
Reviews of Fantastical 2
- Shawn Blanc - The Best Gets Better
- Macstories Reviews Fantastical 2
- Macworld - Calendar app gets more fantastic for iOS 7