Of course one's photographs must speak, or sing, for themselves.
But artists' statements can be interesting and challenging. Thet are written for different purposes. Often, they do not need to be written at all, but sometimes, for books, or certain exhibitions they are requested.
The purpose of the artist' statement usually is to give the viewer of the work an insight into the artist's intentions, and/or a way of better understanding what the work is about.
An artists' statement need not be long. Sometimes a sentence or two will do. A museum was once producing a catalog of their collection. They asked all of the photographers to write something in answer to the question: "What is it you are attempting to do with your photography." Or something very close to that. After writing a couple of paragraphs that sounded like so much b***s*** I threw them away and wrote, "I'm just trying to make the best pictures I can." Simple. No BS.
Now to answer the question: whether to write your artist's statement yourself or farm it out. I think you must write it yourself, to the best of your ability. Then, however, take your writing to an editor. A good editor may ask you to revise your writing slightly, pointing out what needs to be changed, or he/she may suggest you start over from the beginning. A good editor will explain the reaons for each suggested corection. Several, or many, trips to the editor may be needed. A good editor will not rewrite for you, but will suggest ways for you to make your writing better. Go through this a number of times, and assuming you have a good editor, you will, over time, become a better writer.
My wife, Paula Chamlee, and I are publishing a series of books by many of the leading photographers of today, and now, emerging ones, too, in our Lodima Press Portfolio Book Series (see
www.lodimapress.com). For one page in the book, we ask that each photographer write from a sentence to a page, something that enables viewers to more easily enter into the work. We have received writing ranging from a sentence or two to many paragraphs. Most of the writing we receive needs some editing. Occasionally, some need a great deal of editing. We make the edits ourselves and in some cases where we do not feel confident doing a final edit ourselves, we send the writing to our own editor--an old friend who used to teach writing at Princeton. All suggested edits are sent back to the photographer for their approval. They may accept or reject the editor's suggestions. This process may happen a number of times--the writing may go back and forth from the photographer to the editor over and over, until it is feels right to us as publishers. Not all photographers are good writers; some need a lot of editing, but some are excellent writers, and we tread lightly when asking for corrections.
Hope this helps. Bottom line. Write it yourself and have it edited. it is important that you be able to articulate what you are doing and what your work is about.
Thirty years ago a museum director pointed out to me that many of the photographers who achieved the highest recognition also wrote about their work: Edward Weston, Cartier-Bresson, Strand, Steiglitz, Ansel Adams. This person felt that the lack of writing on the part of a photographer was a factor in delayed recognition. There is a wonderful book,
Photographers on Photography, edited by Nathan Lyons, now long out of print (it was published in 1966), but available online, that contains wonderful writing by many of the most important photographers of the 20th century, and if I recall correctly, a few from the 19th century. I strongly recommend it.