I will always advocate for letting your landscape designer refer you to the right landscape contractor. This means that you are going to get someone that the designer has worked with before. The designers reputation is on the line and they would never refer you to someone that they have never worked with. Someone that is licensed, bonded, insured and has workmen's comp.
Now let's assume that you do not need a designer but rather a contractor. Then what? In this video I will share with you how to find your ideal landscape contractor. The different sites that you can go to to find the pro that is right for your project.