I think you are echoing the thoughts of quite a number of people ... and certainly me. In my head the choice is between AGSB and Sale although we actually live a couple of minutes from Stretford Grammer.
My son (and his friend) really liked Sale Grammer .... including talking to all the friendly teachers at the Open Day as well as on 11+ day. Indeed they sat in the car after and said that this would be their choice. I also think that if the Alty school are picking off the high achievers due to reputation then it is more to Sale Grammers credit that they are not that far behind when it comes to results. I also instinctively prefer co-ed .... especially as my son does not have any sisters.
In the other box the facts are that AGSB on the face of it seems to get good results year on year and my son does need a bit of a push to bring out the best in him. Most people we speak to seem to indicate that their choice would be AGSB and that we would be somewhat mad not to take the opportunity if offered. I think AGSB also offers more places for out of catchment too which probably means he has a better chance than for Sale Grammer.
Sorry .... I am sure that this has been of no help to you at all
Just feel safe in the knowledge that all are good schools.