Susie I would think either school is good for your DS, both fab and surprisingly sporty as well as academic schools. Location and ease of getting to is probably the biggest factor. You have a great choice.
PoshDee if your son got in to RGS he can cope with how ‘difficult’ It is. I have 2 sons there both doing fine. In my sons year a whole load left St Georges as they felt the academics weren’t good enough, I know they had call backs and are doing fine if that is what your DS is worried about? You have a great choice too so wouldn’t worry too much about it.