i moved from the ros to the sgs about 6 years ago and never looked back. two 5-6 night stays a year over the last dozen years and the sgs beats the ros hands down
(granted i haven't been back to the ros since i moved- but the sgs location alone is worth it to me).
add to that the fact the general manager of the sgs , richard chapman, is the best hotel manager of any hotel i have ever stayed at. other than saving some money if the ros is cheaper, there is no reason not to stay at the sgs if your choice is a spg property.