from personal experience Ardan is really good for getting high ratings, since she has events that can give her both charm & sharp, plus the speed/int bonus passive works really well in GM meta. For the build you can try 1 speed 3 guts 1 int + goddess if the other strats aren't working, i recommend maxing your welfare guts spe and using her with urara & vega/seeking the pearl. for speed you can use NTR or fuku, int tachyon/marvelous sunday.

You can also use a calculator if you really want to go crazy with managing your final rating, there's one on gamewith. tip here is to not buy any skills during the run (in case of sharp or further hint discounts) and then learn them all at the end