If you hire a professional gutter cleaning company, invest some time in finding the right person for the job. There are a number of service providers available in any area, but not all will provide the best job for you. Why should you have to call out two people to do the same work? Instead, get references and get it done right the first time.
Gutter cleaning should be done at least two times per year. You will want to get out the leaves and debris in the late fall when the leaves have fully fallen. You should also make sure to get back up there in the late spring after the trees have produces their buds and blossoms to get them cleaned out then too.