That all depends on what you want your DoF to do. Given how the staff responsibilities work in-game, you can assign various tasks to your DoF.
What exactly do you want your DoF to do? Sign young talents, sign senior players for the first team, manage your scouting assignments?
Regardless, Pantaleo Corvino is a brilliant, well-rounded DoF if you can afford his wages.
Edit: When searching for a Director of Football, you might want to take a look at potential candidates information page. Some staff will have notable tendencies, and it would be wise to hire someone whose tendencies are in accordance with your own philosophy. I.e, if you favour a transfer strategy of signing young hopefuls for the first team, get a Director of Football who prefer to sign young players for the first team.