which formula the better?  3-18-18 or 6-24-6 for corn

My field are both p and k low testing


I am myself prefering 3-18-18 because the higher k but the salesman is still sugggesting me 6-24-6 and in neibourhood most people are using 6-24-6 too.


I think 3-18-18 is higher price.  


In the past I have been using 10-34-0 but now I want to have some  K .