I'm sure you know this, but with triple science you have nine exams overall. With additional, you still do the first 2 units of each science, just not the third, so you only have six exams. Personally, I found additional science difficult enough, but I'm not particularly interested in science nor do I enjoy it. GCSEs are all about choosing subjects you are truly interested in, and really don't impact your career choice in anyway, they're about getting into the sixth form or college of your choice. So thats also something to consider. You might find it easier to just do additional science and get two decent science grades, rather than doing triple and not doing as good. But that just depends on how much you enjoy science and how well you believe you can do. All you need to worry about with GCSEs is choosing four subjects you enjoy and know you're capable of doing well in. Just do whats best for you, not what people expect of you!