I was born and raised in Toronto and I live in Boston now. Personally, I'd pick the city I had more social connections to because that makes me happiest.

Boston is better in a lot of ways that people have mentioned: ocean, nearby mountains, history, more character in the architecture, weather is slightly better (but sunlight hours are worse), sports teams.

Toronto is better in one major way that I haven't seen mentioned here: food. Toronto has more ethnic diversity and the food scene is where that really shines. Also, if you belong to one of the ethnicities that's more prominent in Toronto that can mean a lot.

The healthcare in Toronto at the high end is worse but still really good and likely better for the lower income levels. Most importantly, taking health insurance out of the picture is a huge stress relief.

Education is the same to a lesser extent. The school system is less important when you're moving to a new area in Toronto because the extremes aren't as severe.

Toronto is also bigger and importantly the biggest city in Canada so it draws talent from the whole country. I think the art and music scenes are a bit better in Toronto but both cities are pretty great in that regard.