I thought there was only mediocre chain-store pizza in Mississauga, until I found Alexandra Hut, 19 Dundas Street, just east of Hurontario. (They have a second location near Eglinton that I have not tried.)
Fresh ingredients, huge variety of toppings, handmade dough - altogether delicious pizza. They deliver, and your order shows up promptly and correctly.
I've only tried the thin crust, because that's what we prefer, so I can't vouch for the thick crust. But the thin crust is excellent. They will even bake it well-done if that's your preference.
I'm from New York City, where people are fanatical about pizza, and most of the pizza I've eaten in Mississauga has been pretty awful. Alexandra was such a great find for me.
On a personal note... I used to use Chowhound in NYC, where I am from, back when it was a text bulletin board. When I first moved to Canada, folks here at Chowhound were really helpful to me in finding good food out in the suburbs. Thank you!