Why do you have Defoe and Fletcher in your team?
Anyway, it's best to find the best striker roles for each of the players, but rotate them every four to five games. That way, they all have a chance, and if they play poorly in those roles, then you can change them. Look into their PI's (Player instructions) and tweak them to give them more freedom, or restrict it. It's important that you do this because it will help you learn about getting the best out of player.
For example, putting the Mentality and Creative Freedom sliders mid-way through for Carlos Tevez and the Closing Down slider all the way up, then you can see him drop deep and roam into space, whilst also having Roam From Position ticked. He could have the Complete Forward, Support role, or Defensive Forward role.