The academic/social balance you seek is probably the norm with fortunate students who have gained acceptance to an elite New England college. I know one young man who has completed his freshman year at Dartmouth and two on their way soon, including my daughter. They are all excellent students, and none of them are party animals-at least not yet. 
Actually, none of them are drinkers, to my knowledge. The current student does report that despite efforts by the school to integrate students of different ethnicity, kids do tend to hang out pretty much with their own. In other words, Hispanics with other Hispanics, etc. I suggest you focus on the things you want out of a school, rather than what you don’t want.
With Dartmouth, the draws for me would be the location, opportunities for outdoor activities, and the school’s strong commitment to undergraduate studies. Best of luck!