I too use a third party app for my iPhone; can't stand the native app. For what it's worth, I use the very intuitive Calvetica.
I've not used QuickCal, but have read it's a great app as well.
I've used NotifyMe 2 for a long time, then I realized that for ToDos I prefer the calendar. Mainly because I can add items to my calendar from any computer, in iCal, quick cal, ect -- it all goes to my google calendar. that said the calendar app for iPhone is poison, so I use calvetica to add items on the phone