I think it's better to make a complaint in person. When you talk directly, you can solve problems faster because you can explain better and they can ask questions if they don't understand.

I prefer to make complaints in writing. It's good because you have a record of what you said, and you can think about what you want to say before you write it.

It depends on the situation. If it's something urgent, maybe talking to someone is better. But if it's a big problem, maybe writing is better because you can keep a record of everything.