I love Billy Bishop Airport! Located right downtown, this small airport offers regular domestic flights with either Porter or Air Canada.
Getting here is easy enough, either take a cab or the shuttle bus from Front/University (outside the Starbucks, clearly signposted). From the dock, take the ferry (5 minute ride). There will be a pedestrian tunnel soon which will make it even easier.
Once you are in the airport itself, there are lots of check-in desks and security moves pretty fast. At the gate, there is a Porter lounge with free coffee/tea and snacks while you wait for your flight.
This is a much more attractive option than Pearson, and will be made even better by the pedestrian bridge and (hopefully) Porter's expansion and new planes.