Interesting (and very good) choice. LBS is obviously the better school, but you are very wise for reconsidering everything because as you yourself mentioned, it's not just about "better" but about you reaching your goals. I am wondering, if attending LBS with it's location and obvious Finance strength, might see you return to your previous industry after you graduate (it would be so easy and also so lucrative). On the other hand, Oxford does seem to have a few more Tech elements in their program. Tough call here. (although leaning to LBS for prestige reasons is tempting)

I would suggest talking with people from both schools who have graduated and are in the sector you wish to enter, because they will give you the best evaluation. If you can also get informational interviews with some big tech/telecom companies in the area, and speak to them about who they recruit, that might also be a good idea. And finally, speaking to the schools specifically, telling them "look I also got an admit at place B, and I would really like to find out more about what opportunities there are in Sector X to help me reach my dreams" If you are kind and civil, they can be very helpful (Of course you can take everyone's advice with a grain of salt )