Boston is historically a center of culture and education. The inhabitants of Boston have access to some of the best private tutors available, as well as the advantage of the large tutoring companies. Those who study in Boston will have no trouble finding a great tutor.
Los Angeles is the largest city on the West Coast, and offers all of the amenities of any large city. There are several large tutoring companies in Los Angeles that offer sessions at the learning center or in the home.
Portland is one of the largest cities in the Northwest. Portland is home to several universities and colleges. Portland is a city very focused on education, and many tutoring services are available either through the colleges or via the established tutoring companies.
These are only a few of the best cities for finding great tutoring services. Keep in mind, that almost any large city will have similar services available. If you live in a rural area, it may be necessary to travel to the nearest city to find a great tutor. Small towns may have some great tutors, but they may be harder to find or over-booked.