Higher concentration of tretinoin or Retin-A should result in slightly greater collagen production, smoothing of skin texture and pigmentation. What is more important, however, is tolerability. One should use the highest concentration that is well-tolerated on a regular basis. It is of no use to apply a super potent retinoid that is so irritating that you cannot tolerate or cannot use more than once in a while vs. a nicely tolerated and perhaps lower-concentrated retinoid that you can use on a regular basis. I personally recommend Kinerase tretinoin which has a nice hyaluronic acid emollient built into this tretinoin 0.05% gel formulation.
Web reference: http://www.drwilliamting.com/Cosmetic_Dermatology.html