I'd like to choose the calendar on "Quick Add" instead of modifying the event details once after adding. Is it possible?
There are 2 ways to quick-add your event:
Open the Event "pane", clicking on your calendar, or by pressing Shift + c
Open the quick-add box, by pressing q
There is no support for choosing default calendar for both #1 and #2. But with #1, if you uncheck visibility of other calendars, then you event will go to the first visible calendar, which is sort of workaround to pick default calendar.