I'm a third year at KCL, and if I could go back I wouldn't go here. It does have some positives, for example being in dead central London is lush, but imo the negatives far outweigh the positives.
It's drained all my money. Like seriously, unless you're rich I would not go to London. If you do, be prepared that you'll either have to spend a fortune living in centre or travelling in every day. I know most people travel for work but it's not the same, if you want to experience uni life properly you need to be near campus and that's hard with King's. Also because we have so many campuses and most people don't live nearby it does always feel quite segregated, it's harder to make new friends because their isn't a 'campus feel'.
Furthermore, although KCL is seen as 'prestigious' this is more due to the fact they have high quality research, as student satisfaction is seriously low. Obviously it depends on the course, but my teaching quality is pretty poor and lecturers care more about talking about their own specific research than actually teaching us.
So yeh, I don't know anything about Warwick but if I had the choice again I wouldn't pick King's or any uni in London. In some ways it's great to get the 'London' experience (so many things to do, see, go out), but I dont feel like you get the 'uni' experience.
EDIT: in terms of grad prospects though, yeh, they're pretty good. I do have a grad job lined up for when I finish.