Ultimately you have to make the choice yourself based on the very different experiences you will have with the different locations and course structures. Academically, there is no meaningful difference at all between the two. Rankings don't matter, and if where you attended does end up mattering in a hiring decision it will be based on that person's subjective opinion of how good the university is, in which case KCL as the much older and much more famous university might win much of the time. There is literally zero chance they will even know the rankings, let alone care.
That all being said, really it comes down to the opportunity cost of a year in industry vs living in the place you want to be. The former is often very useful for securing good employment when you leave - with people sometimes being offered a job at the placement company for when they graduate - and you can always live in London later in life as that is where most jobs will be anyway. Moving to London in a skilled profession is very easy.
There are no right or wrong answers from a UK perspective. I cannot speak to how reputation might differ in whatever country you plan to work in as it is certainly more of a factor outside of the UK.