There is no difference between the economics subjects you take in the two courses. They are the exact same classes - same names, same content, same times, same lecturer.
The only difference is your choice of electives.
In the B. Arts (Economics), you have a free reign to take as many electives as you want from the arts faculty. You also have a limited selection of subjects from the business school (if my memory is correct you can only take Management and HR as electives from the business school).
In the B. Economics, you have a much greater range of business subjects to choose from - you can take commercial law, marketing and finance to name just a few. You can also take Arts subjects, but you can only take 48 credit points worth of Arts units (this means if you complete an Arts major, you have no arts electives).
Basically, if your interests lie in the humanities or social sciences, B. Arts is for you. If your more interested in the business aspect of things, do the B. Econ. In the end, both are pretty much equally employable in the field of economics, as they equip you with the exact same set of economics skills. I guess some employers may prefer the sound of a "Bachelor of Economics" over a "Bachelor of Arts" on a resume, but as long as you're able to demonstrate that you have all the skills of an economics graduate you should be sweet.
Also have a think about what exact field of economics you want to get into. If you want to get into government or public policy, the BA will afford you more freedom to take subjects in things like government and international relations, political economy, or social policy. If you want to work at a financial institution, the B Econ lets you study finance which would be of great value in that industry.
If you're planning on doing further study, I would definitely recommend the BA. It allows you to explore a wide range of interests and gives you a much more holistic understanding of the functions of society and the way the world works, before you knuckle down and hone in on something more specific in your postgrad study. It will make you a more complete person - that sounds really wanky, but it's true.