It depends a lot on how your team is set up to play. There isn't a 'right' answer or a 'wrong' answer.
In a 4-2-3-1 formation where you already have an amazing AMC/MC behind the striker, getting Cesc to play a defensive playmaking role (Alonso) or even a more box-to-box role in the classic Brazillian style (Falcao) might make sense.