I'd probably say Religious Studies, if you can get your head around retaining all the information, because it's a fact-heavy subject and you need to remember most (if not all) of them. However, the good thing is that (as far as I know, in all exam boards) it's got no coursework so all your topics are exam-based. If you're naturally good at essay writing, it's definitely the subject for you.
But I want to stress that you shouldn't do a subject just because it's an easy high grade. You should do a subject which you're genuinely interested in and, if you want to go to uni, applies to your subject and you can show off/talk about in interviews and applications and such!