I would agree that Stihl has the best hand held power equipment out there, but that does not mean that they are not a professional from not having it. For example here most of the larger companies use Red Max. Probably not because they want too, but more than likely because they got good pricing on a bulk deal. They look just as professional as anyone running a Stihl. And by the fact the company makes over a million dollars a year others must think they look professional also.
To me run what you feel comfortable with until you can buy better commercial equipment that can take years of abuse. I do however agree with Ric that you want to have a professional look about you when you pull up to a job-site. Such as but not limited to nice equipment maybe dressed in a uniform, having a clean personal appearance, running clean equipment and just being organized by not having three people get out the truck and look around at each other for five minutes wondering who is going to do what.