Front or Back wall diffusers

Talk to GIK.  They’ll give you some good advice given your room and offer products that are relatively reasonably priced. 

It is recommended that the wall behind the speakers be reflective in nature, so that the sound develops properly. On the contrary, the wall located behind the listening position should be absorptive, so that the rear reflection of the sound does not interfere with the perception of the stereophonic image.

 

Weird how you seem to answer your own question.

@avl1947  I agree with you. Absorbion behind the listening position. I'll add that the corners of the front and side walls will often need bass traps or absorbion panels. This not only controls bass, but helps create and shape the soundstage

Without more info, you only will receive useless advice. Need to know speaker position, listening position, etc.  

@avl1947 

It's obviously room dependent. In mine diffusers/absorbers on back wall and diffusers only on rear of both sidewalls. Also diffusers at first reflection points on sidewalls and absorbers right next to them on second reflection points. Plus diffusers on ceiling between listening chair and speakers. Hardly any diffusing on front wall specially since speakers are 54" from front wall. I believe many audiophiles put diffusers on front wall because they like to look at it. To each his own. I go strictly for sound. You questioning the matter is smart. You can see most of my acoustic setup on my house of stereo system. Enjoy the journey.

Also, about 6 years ago, when drawing the original plans for the house of stereo, GIK told me that the front wall should be addressed last if at all. Just saying.