I used Centennial because my father, a very handy guy, was a big fan of their product. They have won national Energy Star awards for their self-manufactured product and they have an unlimited warrenty on their products for the lifetime of your home (even for new owners if sold).
Their sales staff was informative and helpful, even making a second trip to change an order at my request. "Don't pay for 6 months" financing was arranged without question and the install was quickly booked. The installation workers were professional, tidy and quick.
Even more significantly, my father had noticed an air leak around one of his 5 year old windows after an EcoHome audit. He called them and they came out quickly and spent 3 hours checking all the windows and repairing the affected one at no charge. They even sent him a $100 check after learning he referred me!
So - bottom line is the windows cost more than anyone elses. I was kicking myself for spending that much money but in the end they are totally worry free and for my family that is probably worth the cost.
Note that this review applies to Centennial Windows Ltd in London at 687 Sovereign Rd.