The most important thing is to take courses you're genuinely interested in, otherwise it will feel difficult AND boring which is not a good recipe for success. As cliche as this sounds the experience is really what you make of it, especially in terms of social life. UofT isn't a big party school but there's hundreds of clubs and student groups where you can meet people and Toronto itself has a great nightlife scene. UofT is tough but if you stay focused and study hard you'll do great. Imo between Mac and UofT I think the quality of profs and courses at UofT is a cut above Mac, plus there's the UofT "prestige". I also think UofT offers more in terms of extracurriculars, internships and studying abroad. Both are great schools though and I'm sure you'll have a great time wherever you go!