I use Agenda One and adore it. Once tweaked, I find it's easier to add appointments on my Q directly than from Outlook!
All of the programs you mentioned use the built-in calendar as their starting point, so if you uninstall, all your appointments, contacts, and tasks are still there; you just go back to the calendar application that now exists.
Use the trials...to each his own, and one will surely be "the one" for you!
