Since I am writing reviews for cab companies now...I will write about the best cab company in the city. Unfortunately, they will not pick you up from outside Montreal, but if possible I would use these guys first.
The drivers are always courteous, they do not fuss, complain, or fight me when I use my credit card, (unlike MOST other cab drivers in Montreal I've used). They take me the quickest way, even though I probably seem like a tourist when I am downtown.
I use this company a few times a Month and would highly recommend them.