Media Studies, Business Studies, Economics or History?
First of all, think really carefully about Art. Even if you love it, it will take up all your time and distract you from other subjects when it comes to pre-exam revision. If it is purely a hobby, leave it at that. Don't turn something you love into a nuisance. If you really would like to go into a career in Art go for it - but put the work in early at the start so you never end up lagging behind and missing deadlines. If you are good at other subjects, dedicating your time to Art shouldn't be too much of an issue, but if you really struggle with core subjects like maths, science and english you might need extra time to get good grades, something art might take away from you.
I did Media Studies GCSE WJEC exam board, and absolutely loved it. We had to create a DVD/Magazine/CD cover for our coursework and the exam for the WJEC media board is based on one aspect of media. Mine was advertising, this years is film trailers. In the exam I had to analyse print adverts and storyboard a TV advert. It is very creative and a good mixture of essay writing and art. It requires a lot of research into the aspect of media the exam is on. For me it was adverts so it was interesting to research, but I know one year it was tv news shows which is a bit boring. If you are creative it is a good choice, but like you said it isn't really treated as a serious subject. There again, who cares what others think. Universities only really care about core subjects like maths, english and science and getting high grades, so if you're likely to do well in media it shouldn't really matter too much that it's seen as a soft subject. Find out from your media teacher what the course involves and what exam board it is. Your exam board might be different to mine (WJEC) so this might not really help you.
My friends do Business Studies. They have to research different methods of leadership in managing a business, they look at profit, why some product sales decline, how to stock a business correctly. My friends both want to go into medicine so have no need to study business but they really enjoy it. They say it is quite case study based, and the lessons are a bit boring and repetitive, as is the coursework. But because of this they say its quite easy to get a good grade.
Economics is maths based but I've not heard of a GCSE in it before. I would see if your school has an opportunity to do it at A-Level, so at least if you opt not to do it at GCSE you could do it at A-Level. As I don't think the GCSE is quite common, having economics could make you stand out, but only if you want to go down the maths route. Otherwise it might be a bit pointless.
History is probably the most accredited GCSE in your options. It is useful for any essay-based career like journalism or law, or even art history. In my GCSE we study Crime and Punishment through time, Life in Germany during the 20th Century and Wartime Britain. It is interesting, but the exam board requires you to remember a lot of in depth knowledge so it is a really difficult subject to study for and will require a lot of hard work. The exam is also essay based, so prepare to write a lot. I think History is the most useful subject you could take as the analytical and literary skills it shows you have will be useful for other subjects and universities.
You seem like a creative person, so I think you would enjoy media, maybe consider picking it instead of art as it will allow you to be creative but not require as much time. Business is an easier option, but History is more useful and well-recognised and probably better for a journalism career. I'd say choose between Media and History and Art, and maybe business.
The best advice for situations like this is follow your heart. GCSEs are unlikely to restrict what career you will go into in the future. In terms of GCSEs, universities usually expect Grade C at English or Maths, so as long as what you go for won't distract you from passing these core subjects I would say pick what interests you most. You're stuck with them for a few years so don't bore yourself or stress yourself out with demanding subjects. Find out what topics each subject's course contains and look at past exam questions from the exam board you would study in order to help you decide what will benefit you most. Let me know what you go for and if you have any questions about the Media Studies WJEC GCSE or the History EdExcel GCSE as these are the two subjects I study out of the ones you can pick from so the ones I know most about. Good luck.