I used CalenMob for a year.
I really like its GoogleCalendar compatibility, that allow me to work on shared calendars. Unfortunately this app doesn't provide recurrent events support. To get it I have to buy the CalenMobPro app. I decided to invest on it, but customer reviews say that there is a problematic sync bug since the last update in November, and it hasn't yet been fixed.
So I'm looking for an alternative. Free or not, it doesn't matter but I insist on the intuitive interface and the GUI efficiency of the app. It would be nice for the app to be universal (running on both iPhone and iPad), but it's not strictly required.