Is a solid ceiling better for cold, heat, and sound insulation?
I would expect more "storage capacity" and thus more phase shift during temperature passage from the higher mass of the concrete ceiling; in terms of thermal insulation, only the position (between wooden beams, on top of the concrete ceiling) and possibly the material (glass wool / rigid foam) differ. Do you mean by "sound insulation" the concern that the rooms could effectively communicate using the attic as a bass reflex box? - the paneling should be sufficient to keep that below the perception threshold. With all due understanding for the perfectionist fears of (especially first-time) builders, I would not overdo it here - if I remember correctly, the probably permanent intended use of the attic is storage room (?)