Someone above has already gone into great, delicious detail, but I will summarise:
Economics is respected by universities (ie it is a 'strong subject'). It's the study of the economy itself, and is slightly maths oriented. It is difficult for some people, but that means that the grade boundaries will be lower. If you work hard and do extra reading you will do the best you can.
Business studies is a 'soft subject' (ie if you have more than two soft subjects out of your four, say goodbye to any top 25 universities). It is more based on practical application and business itself. People find it easier than economics.
So my advice is to take economics, as almost everyone has recommended so far. It may be tougher, but it will pay off when you go to a good uni.