The concepts you explore and learn about in Economics are specific/relevant to the field of economics. Preliminary Economics covers concepts such as consumers, markets (including labour and financial markets) as well as the government. HSC Economics expands on those concepts by introducing you to the global economy, Australia's place in the global economy, economic issues as well as economic policies and management. There is quite a bit of writing in Economics, particularly when considering Section III and Section IV essays, meaning there is also quite a bit of content to be covered. If you take Economics, you need to make sure you are regularly studying and staying up to date with the content, and seeking assistance with any concepts/aspects of the subject that you feel you are struggling with.
Some advantages I can think of with regard to taking Economics is that this subject allows you to build a foundation of knowledge relevant to the field of economics, which can be useful to have beyond the HSC, such as for your first-year studies in a Bachelor of Business/Commerce with an Economics major, a Bachelor of Economics, and (I believe) a Bachelor of Actuarial Studies.
Business Studies is much broader as it explores different areas of business, where you'll be given the opportunity to build a foundation of general knowledge of the business world in year 11. In year 12, you will explore 4 important areas of business and will study contemporary business issues through case studies and apply the knowledge you acquire to problems encountered in the business environment. Preliminary Business Studies covers the nature of business, business management as well as business planning. HSC Business Studies explores 4 key business functions: operations, marketing, finance and human resources. Business Studies also includes some economics concepts (such as exchange rates) within the Finance topic in year 12 for example. Just like Economics, there's quite a bit of content to be covered in Business Studies, and quite a bit of writing in exams as well, particularly for the Section III report and the Section IV response. In terms of difficulty, Business Studies is generally considered to be easier than Economics because the concepts taught are relatively easy to understand. However, with that being said, you should also ensure you are regularly studying and staying up to date with the content, and seeking assistance with any concepts/aspects of the subject that you feel you are struggling with if you decide to take Business Studies.
The advantages of taking Business Studies include the fact that it allows you to build a foundation of knowledge in multiple areas of business (including economics) rather than only one area of business. This knowledge could be useful for your first-year studies in a Bachelor of Business/Commerce (examples of majors include finance, accounting, management, human resource management, economics and marketing) as well as a Bachelor of Economics.
In terms of scaling, Economics scales relatively better than Business Studies. However, that being said, you should keep in mind that scaling should not be a primary factor to consider when choosing a subject. Instead, you should consider which subject you are more likely to be interested in as well as which subject you think you can perform better at.
I would personally recommend taking Business Studies based on the information I provided.
I hope this helps!