Congratulations on your admits! Really really fantastic job!
Pardon a dumb question, but do you have a UK and US passports? If not, I don't think you could have both roads open to you once you pick a school since few US employers would hire an LBS grad out of MBA and similarly it's a bigger hassle to recruit in Europe out of the US, so once you are committed to a location, that's where you stay.
I would suggest of imagining yourself 10 years later and looking back - where would you see yourself? What matters to you outside of MBA? do you want the world's largest economy and opportunities and pay offs (as well as risks) or do you prefer the more level and balanced lifestyle of Europe?
Comparing MBA experience in Boston and London is going to be tricky. Time will also fly very quickly. That's only 18 months of your life but these 18 months will determine quite a bit in terms of what happens next and where the rest of your life will be spent. If you see yourself staying in Europe, and that's something you are looking for, then I think there is no reason to look at MIT. Similarly, if you are are looking/considering to be in the US in the long term, there is no reason to look at London. I would encourage you to visualize where you want to be and I think there is merit to pick each program. If i were really unsure (and I can tell you that I was when I was applying
MIT is clearly a stronger play (even look at average applicant caliber, average GMAT, etc). You can network your way to a job after MIT anywhere but after LBS, it is London or Dubai.
In short, I would prioritize the content you want to be on after MBA. If unsure, pick MIT.
I know I broke the rules you set so this may be a dissatisfying answer, so feel free to ignore. What do I know, I am just an old man.