We have Active FX, Fraxel repair and Fraxel restore at our Centre and I can give you a completely unbiased answer to your question. If a physician uses the settings that the company gives them for Active FX, the results are usually not that impressive. The doctor can increase the density and energy settings on the machine and treat more aggressively, but this will increase the downtime and is not, by definition, Active FX.
As far as comparing Fraxel repair and Active FX, there is a clear difference. The Fraxel repair penetrates many times deeper than Active FX, so the improvement in acne scars, wrinkles, sun damage, and the degree of skin tightening is much better with Fraxel repair than the Active FX. One treatment with fraxel repair is better than one treatment with Active FX. I have the photos to prove it.
Updated Nov. 13th, 2008:
Sorry I had to cut my last response off to go see a patient. I agree with Dr. Stevens' assessment when comparing Active FX and Fraxel restore. The nice thing about the Fraxel repair is that we have been able to use it safely on darker skin types as well.
For you as a patient, the best thing you can do is find a reputable dermatology/plastic surgery centre that offers all/most of the possible technologies that may help you. Ask the physician to see before and after photos of his own patients. If the physician can only show you photos from the laser company or other doctors, that should be your clue to go elsewhere.
Check on the physician's board certification. Lastly, the physician should be performing the treatment on you. If he/she is delegating the treatment to someone else on his staff, such as a nurse or "laser technician", I would go somewhere else. These treatments can have serious side effects and should be performed by someone that has extensive experience and formal training in this specialty.
Good luck and take care.