I think if u pass the key subjects maths English and science that’s all that matters.I haven’t heard colleges and uni’s looking at how many subjects you have done. So I guess the higher grades is better.
What would look more effective when I apply to college and universities and on a CV - 6 GCSEs with higher grades or 9 GCSEs with lower grades?
Ermm. Well I'm pretty sure Uni's (Some not all, look into that specific uni for more info) look at GCSE grades as a prediction for how you did in ALEVEL. Since you still don't know what you got in Alevel, and only have AS grades and GCSE grades, but they will most likely look more at the grades you chose for Alevel, but I'm not too sure.
Colleges only really care about maths, english, and the grades for the subjects you want to take.
What would look more effective when I apply to college and universities and on a CV - 6 GCSEs with higher grades or 9 GCSEs with lower grades?
Well it depends, unis look at gcse and a level grades and then look at the subjects youve chosen, make sure you pick good ones and ones you can get A*'s on