I agree with both Working and Banana. At this stage DS was clear he much preferred the Hogwarts-type feel of W over the playing fields of St Pauls, whilst was never tempted by Eton, in part because opf a couple of very confident characters who were headed that way. (And partly because it had never crossed our minds that we as a family could "go to Eton", plus the fees....)
I have met a couple of Eton mothers who have said that in retrospect they should have send their second sons to W. What suited their elder was not right for their younger. Eton is a big busy school and a quieter academic boy can get lost, and might have preferred to have stayed at home. I've also heard W mums say the same. Their second sons were less suited to the "being a geek is fun" culture. I met one mother who had sent her three sons to all three schools, which seemed like an impressive investment in uniform.
Our son was absolutely happy at W. It was a perfect fit and he has made what I expect to be lifelong friends. I agree with banana that the presence of bright and hardworking girls in the sixth form is a huge plus. Add in the great teaching, the existing culture, and the amazing Central London location, and the final two year become something very special. DS more or less kept boarding hours, going in for breakfast and doing his homework in the library, and seemed to only come home to sleep (or play computer games.)
Which school makes your son's eyes light up? Does he have a good friendship group going onto W. (I say this because being at the junior school appeared to be a bit of a two edged sword. Peer impressions seem to have been formed early, and a couple of boys who were probably imature at 7+ never got a chance to reinvent themselves and might have been better off with a fresh start.) Does he want to board.
Both choices are good ones, so your son is unlikely to make a bad decision. There will, whatever the Eton posters say, be a small number of boys who dont enjoy their schooling at either school. The risk of this is less if your son is allowed to make the choice, and you then avoid him turning it back on you. Plus a safe start in a process of him taking control of his future.