I was in an office that used BusyCal a long while ago but didn't have to support delegation.
App overall back then worked great and has a fee trial for you to test out at least.
I understand, as I'm pretty picky, too. :-)
I'd like my calendar apps to be platform agnostic, too, but one program that runs on all platforms doesn't exist, and so I'm settling for common, shared cloud calendars. I happen to be using iCloud, but that's mainly because google got rid of push calendars for free google accounts. As a result, I'm using three different apps/programs to access my cloud calendars:
Pocket Informant, on iOS devices.
Busycal on OS X. It's also the only way I've found to add/edit subscribed iCloud calendars (not shared calendars, but subscribed ones, like these).
Microsoft Outlook 2010. Yeah, everyone hates it, but it has the most power.