I'm currently in the situation of having to choose between the two options aforementioned in the title. The field of study I look forward to pursue is Computer Science. I would say that attending a course which offers a MComp would provide me with a deeper knowledge and a more elaborate skillset which I can employ after I finish my studies. However, I also have the option of pursuing a BSc at a top-ranked university which would probably provide me a higher-quality education. Moreover, the difference regarding rank (and supposedly quality) between the two universities is not big (namely, only a few places).
To sum up, which path should I choose for my academic preparation ?
If you can attend a top university, do so. Having other excellent students around can provide a much better learning environment--to the point that in three years at a top place you may learn as much as in four years at a more mediocre institution. If you do well, you can always do another one or two years of graduate study after your bachelor's degree.