Which of the aldehyde is most reactive towards nucleophilic addition reaction ?

Both aldehydes and ketones are very reactive towards the Nucleophilic addition reaction, because carbonyl group is a very reactive group. So, the reactivity of the carbonyl group can be decided the magnitude of the positive charge on the carbonyl group. So, the compounds that have least +I and +R group will have the highest positive charge and will have highest reactivity. So, the HCHO doesn’t have any +I and +R group, therefore, it will have the highest reactivity.