First off, Congratulations!!!
There are so many differences between the college that can help you out with the final decision.
1) Financial :- Tution fee/ Livings costs - In addition to the tution fees, living costs in London would be higher compared to living in Cambridge and that too for a longer time
2) 1 year program vs 15-21 month program - You got to look at the years of work ex you have. If you have significant work ex, you might want to consider 12 month program as Internships are not going to help you out much and otherwise
3) College focus - LBS is more Consulting focused vs Cambridge on Entrepreneurship. LBS is also very good in Finance domain. VC is pretty tough to get into right after MBA if you do not have relevant work ex already. Good if you have, but I think both Cambridge and LBS can help you out well there. I would assume LBS will have more alumns in VC compared to those from Cambridge
4) Class size - 500 vs 200 -> See which one would you be more comfortable with
5) Social aspect - Cambridge is supposed to be a better fit if you tend to look at social aspect because of the College based university. LBS on the other hand based in London and that it doesn't have college based system will score a tad bit lower on this factor
6) Brand - LBS undoubtedly has a much better brand name for MBA than Cambridge. This will also come to light in terms of alumni as you will find many in the relevant industry and will be able to help you in getting in your desired industry. Cambridge's alumni on the other hand is spread across multiple disciplines which is especially helpful if you consider Entrepreneurship for instance, as it would require you to collaborate with people from different disciplines.
You must have done a lot of above research already though I hope it helps you a bit in making a right decision. Ofcourse, in the end you can not go wrong with either. Everyone wishes to be in your shoes.