I'm an engineer in my first year at Cambridge. I applied for general courses because I couldn't decide which branch I liked. I suppose a general course is more demanding, since they teach you more stuff. In fact if you compare two graduates; one who did a mech eng course, and one who did a general course later specialising in mech eng, they would both have the same standing in mech eng. But the general eng graduate would have also know more about the other disciplines. So in that respect general courses could be seen as harder. I'd say general courses are more interesting and more useful, especially if you can't decide on which type of engineering to go into.