Although I much prefer Billy Bishop's airport (because it's a hop, skip, jump from my place), I can't really knock Toronto Pearson. It's huge which spaces the crowds out, is always clean, has lots of restaurants, bars, convenient stores and anything else you could think of needing. And although it's a large airport, the layout is well thought out and very easy to navigate through.
Their pet relief areas are also easy to find which is key for owners like me that travel with their loved one, and the employees seem to be generally friendly.
I don't have anything bad to say about this airport as I've yet to have a bad experience in the year that I've been coming here. I'm taking 1 star away because it can be difficult to drive to during rush hours and is not downtown like Billy Bishop. All and all, just plan ahead and you shouldn't run into any problems!