If you have a choice between YYZ and YTZ then there is no choice. Fly in or out of here. The lounge they have while you are waiting for flights reminds me a lot of the VIP lounges for the usual suspects of airlines in other airports but here it is the default -- nothing to be a member of.
The ferry ride is laughably short and when the pedestrian tunnel is finished that will be a perhaps better option but I think it will probably take about that same amount of transit time.
Bottom line -- if Porter can take you where you need to go, use them!