When I want to make a complaint about a defective product or poor service, I would rather make my complaint in writing. Writing a complaint allows me to organize my points of argument in a logical manner. If I'm really unhappy with the way I'm being treated, I want to present my reasons clearly. I don't want there to be any confusion about why I'm complaining. I like to list my complaints and then list supporting examples. That's the best way of making sure everyone is clear about what I'm saying.
Putting my complaint in writing also ensures it won't seem too emotional. If you feel that you've been treated badly or taken advantage of, it's easy to lash out. Losing your temper, though, is a sure way to lose your argument. Yelling is very satisfying at the moment, but it only makes the person you're yelling at mad at you. It doesn't get them to agree with you or to offer help.
There's also the issue of the person you're dealing with. If you complain in person, you have to talk to whomever is there. Chances are that he or she isn't the person responsible for the defective product or the poor service. Often the people who take complaints are not the people in charge, unless you're dealing with a very small business. Yelling at them isn't fair, and doesn't do anything to get a refund or satisfaction for you. You need to reach the person in charge. The best way to do that is in writing.
Writing about your complaint and sending the letter registered mail also gives you written proof. It's clear that you tried to settle the matter in a reasonable manner within a certain time period. This way, if you need to take further action, you have physical evidence of your actions.
Writing a complaint has the advantages of organization, effectiveness, and fairness. That's why I prefer to write rather than personally present my complaints.
I would actually prefer not to complain at all, and in cases where it is really necessary to do so, I would most likely complain by phone.
Although, in order to stay within the topic let us compare two given possibilities; complaining in writing and complaining in person.
Complaining in person enables us to interact personally with a real person who represent the company where we purchased a product from. This method of complaining definitely gives certain advantages as opposed to complaining in writing. For instance, one can always ask to speak with a manager if he would find a clerk's answer not good enough. And this approach also enables us to take the reason of complaining with us and actually demonstrate to the manufacturer or seller what is the actual problem is.
On the other hand, complaining in writing has its own advantages and could serve as a very powerful tool to a sophisticated complainer who knows how to fight for his rights. Firstly, words written on paper could serve as a latter proof in court, if, of course, the dispute would go that far. Also in some cases the company we purchased a product from may not have live representatives available in your region, and therefore, complaining in writing could save you unnecessary long trip. Finally writing a letter with complains could save you a lot of aggravation that you always risk to get by complaining in person.
I personally prefer to complain as less as possible, although if I had to choose from two forms of complaining, I would choose to do it in writing.