I would avoid a school with a commute in excess of an hour, I don't think it worth it. With regard to grammar schools, being a grammar school does not magically make it a good school, there are some dodgy ones out there. I would recommend comparing the progress 8 score of schools. Progress 8 is a rather flawed metric when used in schools, but I think can provide an interesting comparison tool for parents. Basically, if the P8 score is positive, that school is above average for GCSE results, if it is negative it is below average and a score of 0 is bang on average. Now, Kent never lost its grammar school system unlike the rest of the country. This means that there are a lot of grammar schools, but not all of them are great. By comparison, across the Thames in Essex, most of the grammars got purged, but the result is that the few that do remain are pretty damned good. Time for some direct comparisons.
This Grammar school in Sittingbourne, Kent has a P8 score of -0.42. This means that compared to other schools with similar students, those at this school on average dropped about half a grade across their subjects at GCSE.
www.compare-school-performance.service.gov.uk/school/137800/borden-grammar-school/secondary
By comparison, this grammar in Essex has a P8 score of +0.85, meaning on average being at this school added almost a whole grade to the students' GCSE results. The school will actually be disappointed with this as last year it was +1.1.
Finally, a decent Kent comprehensive. Note the P8 score of +0.31.
www.compare-school-performance.service.gov.uk/school/136456/rainham-school-for-girls/secondary
I would say overall, good grammar > good comp > bad grammar > bad comp. So what have we discovered? Good schools are good and bad schools are bad. How profound.
Seriously though, I would find a decent school (comp or grammar) within 1 hour of your house that your child thinks they would feel comfortable at (so go to open evenings).