Mazatlan has a lot going for it. It's toll road all the way down, so it's easy driving. Mar Rosa is lovely, and right on the beach. The city is fun, too. There is a great tourist area, plus the regular "Mexican City" part. We seem to spend about a week in each direction there. Not too many years ago, we spent two entire winters there. It's warm enough, and the ocean is not too cold, either.
For a first trip in Mexico, however, I don't recommend making the run in just 2 days. It's about 500 miles from San Carlos to Mar Rosa. Take enough time to learn how to buy gas, pay tolls, get to the parks, and not be stressed. 3 days, or even 4 would make it really really easy.
