Religious Studies is not a traditional subject. However History is.
In doing both at AS (having not doing both at GCSE) it was a new, nice experience for me. I think it really depends on what you like. I ended up dropping history just simply because it was too narrow and only focused on certain someone (Mussolini) which to me, was not History. RS, was way more varied. I'd say History had way more content, but RS was more varied, thus being more entertaining to actually study. I still don't get half the stuff I learned at AS, and hardly understanding ANYTHING in A2, but I think it's far much more interesting than History.
Just depends on what you like to be honest. I'm sure your college or sixth form will have an induction day (usually in July) to give you a "taste" on what you shall be studying. If you don't get the chance to choose the subjects you want to be in, then come Sept you should have an allowance for up to 3 weeks to swap and pick your A-levels.