It is always diffcult to know what to base the choice on as so much can change. Either with the school itself, or from a higher influence.
For DD1 (now yr 11) we had a realistic 'choice' of 2 averagish comps. Not much between them in the league tables.
DD1 was at the time science mad and keen on music.
Our first choice was the school that had a sixth form, offered triple science, more than one MFL, and had a better head. The other school had a Performing Arts specialism, alhough dd not appear great on music. Never thought of asking whether triple science took up an option, or whether any GCSE's are sat early or modular/linear.
Fast forward 5 years, she is taking the triple science (at the cost of another option), not altogether happy about the GCSE's/modules she was forced to take in yr10. And now being music mad, not struck with the facilities and attitude to music at the school. Also, whilst having a sixth form is a bit of a security blanket in a competitive area, she would have to compromise subject choices to stay as the option blocks are so limited.
The head in the other school has also since changed for the better. I have heard they now offer triple science too.
Next year, we will face the same choice for yr5 DD2. Also in catchment for a superselective, but not sure we want to put her through it. (Streets ahead in literacy, especially writing, but maths very average).
We will be going to the open evenings for both schools this year and next and keeping a close eye.
As for specific questions - not a clue. Final choice likely to be down to gut feeling alone.