I have settled on TaskTask HD. My company uses Outlook 2007 and Exchange. TaskTask syncs up and supports Folders, Categories, Reminders, Repeating Tasks better than any other app I have tried.

I dropped the GTD add in due to incompatibility, and synchronization problems. But I set up the same Categories such as @Office, @Home, @Agendas. I use Folders for projects and TaskTask is the only app I found that keeps everything sync'ed properly.

iMExchange supports tasks but not as flexible. However iMExchange supports Outlook Notes which TaskTask does not.