Congrats on your acceptance to both places. Some things to consider :
London - cons
*London is extremely expensive to live in
*work visas for non-EUs are very very difficult to get
*the UK might as well leave the EU . A likely referendum in 2016 is on its way, and a potential leave has the potential to severely hinder the economy, at least in the short run.
*Competition for jobs in London is beyond brutal. Even with an EU passport, literally you will be competing with thousands for one place.
* The UK is currently one of the highest exporter of ISIS fighters. The country has pending problems with the ethnicity-based crime.
London - pros.
*Amazing city to live in and work in - rich history and gorgeous architecture. Many things to do
* Income in pounds is really sweet.
* Access to a whole host of amazing cities in Europe.
* LBS obviously has better international reputation
* LBS attracts absolutely the finest banks/consulting companies in Europe whereas Cornell faces much stronger competition in the US.
Personally, I would opt for UCLA. If you are not admitted though, it really depends on your nationality and career goals