There are many great tours to take either on your own or with a professional organization. I do some of both and it just depends upon the interest of the gals on the trip, the time allotted and the time of year we go on the trip.
Make sure you consult websites and read reviews before booking and check their cancellation policies. What happens when someone in your group is ill? Can you change the day or receive a refund within a certain deadline?
Will your tour be a large group or small? What language will the tour be given in? Personally, I detest taking tours with large groups of people with everyone having headphones in their ears. Part of the fun should be having conversations with the other folks taking the tour with you.