51Talk and Acadsoc are both legitimate and reputable online English tutoring companies. Both companies offer flexible schedules, competitive pay, and a supportive teaching community. The main difference between the two is the range of services they offer. Acadsoc specializes in one-on-one tutoring services for individuals and small groups, while 51Talk offers both one-on-one and group lessons, as well as additional services such as business English and test preparation courses. Ultimately, it is up to you to decide which company would be the best fit for your needs as a teacher or student.