Using a local one has the benefit of being able to meet with them face-to-face - you know what you get, in a way. But if you are shopping around, there are plenty on the internet, both large "faceless" agencies and smaller ones.
Remember that "you get what you pay for" is true of travel. You may want to get several quotes from different agencies and then decide which one you feel best about working with, and book through them. The lowest price might not mean the best service - and vice versa.