I go to UofT. It's great. The only 1,500 person lecture I've had was the big first year psychology course (which is an elective), and honestly it was great. The quality of lecture you get at that size is incredible. For CS courses, most of my classes after first year top out at 50-60 people. We also have much better professors and instructors then you do at Waterloo.
Beyond that we get to study on a beautiful campus in the middle of a very fun and interesting city, whereas you are stuck on an uninspiring concrete-and-goose-dropping wasteland in a small "city".
I bought the propaganda that Waterloo is #1 when I was in high school. A one-day visit to each campus quickly changed my mind and I am very happy I made the decision to go to the better school.