I will be traveling for Boston into Quebec. Trying to decide if it is better to rent a car in the US or get to Montreal and rent one there?
Car rental in the U.S. probably is a bit cheaper.
Nevertheless, the difference in price is minimal as long as most of the transnational car rental companies have similar pricing models for different regions or even countries.
It is easy to compare the car rental prices/available cars/ car company rating scores or even reserve the vehicle online. You can try it here.
To be honest, if you are flying into Boston Logan International Airport do not bother with a car. The Bostonarea has one of the finest public transportation systems anywhere. Downloadable maps, easy to navigate and efficient. You can catch the "T" right at the airport and get anywhere in the area in a short while.
If you want to drive to Montreal, you can take the "T" or a commuter train from South or North Station out to a suburban location for car rental and rent the car there.
Bostontraffic is ridiculous, parking is a hassle and it is so small in actual area that you really do best on foot or public transit. I lived there for 2 years and never drove.
I have never been to Montreal but if you check the tourist sites, the same may also be true of that city.
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We rented in the US and it worked out great. It would probably be an easier option.