When I first got here, everyone at UofT would rave about Greg's and I would say it is for good reason, they are open late, carry numerous flavours , have big serving sizes and taste good (very very sweet). Not a fan of annoying line ups, price and lack of seating especially if you're forced outside with ice cream when it's cold outside.
Staff treat you fine and some of their featured flavours do sound exciting. I recommend Greg's over most other ice cream parlours in the area, but I doubt it has the claim as the best ice cream in Toronto.