If you really can't decide then do what others have suggested and go for the one which is closest/has the easiest journey. Don't underestimate how tiring a difficult journey can be - especially for a year 7 child. When it's cold, dark and raining and you have a heavy bag, sports kit and perhaps a musical instrument with you, you don't want to be struggling with the journey as well.
DG is more selective so if my son was a borderline pass I'd go for Chis & Sids. Though having said that, I'd probably go for C&S even if he was a top scorer as, while I've no direct experience, it's always seemed to me to be a lovely school. Is he sporty? Does he/you have any views on mixed/single sex schools? Any friends going to either school?
When I couldn't decide between schools I drew up a list of what was important - length/ease of journey, school start time (to fit in with taking younger children), which sports they did, what their specialisms were, ofsted/league tables etc etc and gave each school a score in each category. Interestingly though, I then redid the figures so that I ended up with the school I must have known all along was best for my eldest!