World's best slugger vs world's best pitcher, who would you sign?

Let’s say that you were a baseball manager. Your current team is mediocre with no clear gaps or advantages. You have enough money to sign either the world’s best slugger or the world’s best pitcher. Both are willing to work for you for the same amount of money.

Would you sign the slugger (i.e. batter) or pitcher?

Personally, I would sign the slugger as he would play everyday while the pitcher would only pitch once every five days.