Your army has something to do with it but your opponent has more to do with it. If you're EA and going up against other GP or EA bases, strong footmen or cavalry (or elephants) can get the job done. However if you're up against a well developed EA or IA base, engineers will be necessary.
Also, if you're into quick 'hit & run' attacks using raiders, then 2 or 3 engineers are a good inclusion.