Hello Eraldo, two lovely schools that produce lovely polite, confident and ambitious boys and girls , I agree with Suncrest, and add the following:
Leighton Park-known for excellent pastoral care and espousing (highly inclusive and gentle) Quaker values, higher number of overseas students, no CCF, significantly higher fees, does International Bacc, no uniform, fully co-ed, has boarders, smaller classes. Would be considered to have a very holistic approach . I've always assumed, perhaps wrongly, it's a smaller school than Bluecoat.
Reading Blue Coat-excellent Head, perceived to have a much harder entrance exam, strong on academics, arts and and sport (inc. rowing), uniform until 6th form, co-ed for A levels only (but very small number of girls in 6th form), no IB.
They are both excellent schools with beautiful grounds, and I imagine that your son will be very happy in either-I have friends with boys in both. You may also wish to factor in the journey and your son's views, and plan B if you choose Bluecoat and he doesn't get in. I appreciate that you've already narrowed it down, but assuming your DS is Y5, have you looked at the Oratory?