If you want to stay in Old Montreal, I'd recommend the Hotel Nelligan on Rue St. Paul. You'll love it and they have a great rooftop terrace. Old Montreal has cobblestone streets and lots of activity.
Otherwise, stay downtown at the Novotel on Rue De La Montagne, which puts you within a block of the main shopping areas, restaurants and nightclubs.
Ultimately, either option is just as good, since Old Montreal is only 10 - 15 min walk from downtown (or 2 stops on the subway). about 5 years ago