My personal favourite is probably Pavarazzi's Gourment Pizza, a place with just a couple of stores here in Ottawa. Close second would be another local chain, Colonnade Pizza. We actually have a bunch of local pizza chains, now that I think about it... there are at least two more that I quite enjoy. 
Of the big chains, I tend to prefer Pizza Pizza. It's not fantastic, by any stretch, but it's not terrible, either, especially when it's fresh. Hard to beat the prices, too.
And my preferred toppings: chicken, bacon, hot banana peppers, black olives, onions, and BBQ sauce. I'll often just get the chicken, peppers, and sauce to save money on toppings, though.

Of the big chains, I tend to prefer Pizza Pizza. It's not fantastic, by any stretch, but it's not terrible, either, especially when it's fresh. Hard to beat the prices, too.
And my preferred toppings: chicken, bacon, hot banana peppers, black olives, onions, and BBQ sauce. I'll often just get the chicken, peppers, and sauce to save money on toppings, though.