We looked at both schools - my DS1 is starting secondary school in September 2012, and while originally I was convinced that we would put both schools on the form, we decided against the Vaughan, not because it's not a good school, but because we thought it's not the right school for DS1.
It seems very very competitive and I think if your child is very good at school, it will certainly be a good choice. DS1 is average with a fragile self confidence and I really had the feeling he would sink at the Vaughan.
The Oratory on the other hand seemed really committed to pastoral care, and the good results seem to come as a result of that care.
I thought the Assistant Head at the Vaughan who gave the speech on the open day was horrible, arrogant and obviously playing a game, ie, we are so popular and oversubscribed, why should I try to convince you that we are the best school? With a new Head this might change, and I'm aware that you shouldn't judge a school by the speeches on Open Day alone. But I do think that the attitude of the Assistant Head must filter down somewhere/somehow.
I know boys at both schools and they all seem to report pretty much the same - both schools are strict, but all the boys seem to be proud of their respective school.
Oh, and of course, chances to get into either school are very small - but good luck!