Can I use these interchangeably?
The best defence is offence.
Offence is the best deffence.
The best defence is attack.
Attack is the best deffence.

Question

Can I use these interchangeably?
The best defence is offence.
  Offence is the best deffence.
  The best defence is attack.
  Attack is the best deffence.

Answer

While they all mean the same thing, the word offence is always used in this expression, it's a standard collocation. So if you want to sound natural, you could use either of the first two.

Answer

The only difference is in the subject of the sentences (attack or defence) and therefore the implied emphasis.

Answer

Yes, they're all interchangeable. For spelling, it's 'defence' (not 'deffence')

Ne manquez pas cette occasion d'apprendre une langue depuis chez vous. Découvrez notre sélection de professeurs de langues expérimentés et inscrivez-vous dès maintenant à votre premier cours !