It is rather difficult for me to answer the question how I prefer to complain: in writing or in person because sometimes I just do not have a choice. For example, if I order a product using the Internet from another state or even country I will more likely have the opportunity to speak to a representative of a company in person. So, in some cases I choose to speak in person and in others I prefer to complain in writing. However, I believe that every option has its advantages.
From the one side, complaining in writing brings many benefits. First of all, one does not have to spend his precious time driving, waiting for his turn and talking with a representative. He can just send mail or e-mail and get all explanation he needs. Second of all, I think it is the best way to avoid an unpleasant conversation. Personally, I do not like to complain about anything especially, in person. Finally, sometimes it is impossible to have a face-to-face conversation because a company which provided a poor product or service is too far away.
From the other side, complaining in person has some benefits too. First, this type of complaining provides an immediate feedback. So, if I have some complains about company's products I will receive all information and explanation right away. However, sending a company a letter and getting a feedback can take more then a month. Second, face-to-face conversation is often more effective. People talk to each other, see each other facial gestures and body movements, which can tell a lot about a person. In addition to these practical benefits, in the case if one can not receive creditable explanation from one representative he always can require to talk to another person. For instance, my husband recently had some extra withdraws from his account by his bank and he was not aware of it. So, he went to the bank and explained to the bank's representative the situation and they together found the solution and those money was given back to my husband's account. I think, in this case face-to-face conversation is the best way to complain and get feedback fast.
In conclusion, I think that if I have to complain about a product or poor service I will do it in person. However, if face-to-face conversation is impossible I think I have nothing left but to send a letter or write an e-mail there.