I'd say they are both similar in difficulty and I've done some designing and writing. Being a writer tends to be isolating, you have to get used to being alone. Both professions are judged by strangers, so that can be tough, you have to develop a thick skin and really believe in what you do. Some people are naturals at their chosen profession, so for them, it would be easy!
Start writing! There are books for teens that are very helpful and you'll have a head start on others who want to be authors if you start now.
Good luck!
