Percentage A*-C and top 100 of schools will tell you about the intake of the school population. If you're in an area where the school is genuinely comprehensive, these are not going to be as high as in an area with predominantly middle class children of educated children.
Progress 8 tells you about progress from starting points, so is more relevant in terms of seeing how the school did with a range of children. However, this is only available for 1 or 2 years depending on schools, and you probably want to drill down into the high/medium/low achievers statistics to get something more meaningful. High progress might also indicate a large number of DC that underperformed at primary school!
Personally I found comparing the breakdown of GCSE results most illuminating. It told me, for example, that one school's high A*-C was due to them not entering so many children in harder subjects (e.g. only 25% doing triple science as opposed to 50% at neighbouring school) and that another school seemingly did miracles for the DC on C/D borderline but the results for high achievers were much lower than expected.
However ... again ... bear in mind if you are only looking at one year of stats that this is only representative of that individual cohort, and it might have been a blip year, or things substantially changed since that cohort entered the school.
What I'm trying to say is ... statistics just add to the picture, and whilst it's worth looking at a range of information, this gives nowhere like the whole story.