"Double degrees" or a combined program of study just means you'll get two degrees in less time than if you had done them sequentially. It depends on what you want, e.g. Engo/Commerce. Do you want to take five years to do a Bachelor of Engineering and a Bachelor of Commerce, or do you not mind taking that extra semester to do a Bachelor of Engineering, then the grad entry Master of Commerce? (these are USYD examples). Both Bachelor and Master of Commerce qualify you equally, but some people have a thing for Master > Bachelor. Also, do you want any electives? In the combined B.Comm., you'd get very little, if any, space for electives, but M.Comm. maybe you could.