If you're working downtown, living near a TTC subway station is usually the most convenient option. If you're commuting from outside Toronto, GO Transit is reliable and often the better choice for longer distances.
Areas like Mississauga, Pickering, Oshawa, and Burlington can offer better value while still providing good access to downtown via GO Transit.
For a look at transit-friendly communities, check out:
https://www.gta-homes.com/real-insights/developments/top-condo-projects-near-go-train-stations/