If your main reason for studying the double degree is to easily finish the degree within the shortest time and to earn money easily, then I will advise you not to take the double degree programme. To study with ease and to earn money easily, just go for the BBA degree. There is no reason for you to study the BEng degree if what you want is an easier life.
I am one of the students taking double degree BEng/BBA. But I take Computer Science + Finance, so I don't know anything about Electrical engineering or mechanical engineering. But for your information, there are more choices of electives in Electrical engineering. One more thing is that Electrical engineering is the least popular major this year among all engineering majors. Finance is better than Marketing in Hong Kong, but if you are that type of person that can influence people, you can consider taking Marketing. All double degree students that I met so far take Finance as their BBA major.
