Which is best treatment and why? Z-plasty or w/plasty or something else? (Photos)

First, let me say that I am hardly surprised that you found the fraxel treatments to be of little value. Anyone who has read my answers to numerous questions knows that, in my experience, these supposedly "next best thing" to come along, relatively expensive devices are proving to be far more backed by manufacturer supported marketing hype than hard science. Before considering excisional surgery of any kind, you might consider relatively inexpensive subcision lifting combined with the use of a biostimulatory filler to raise up the depressed portion of the scar and make it more flush with the surrounding skin. Subsequently, if so desired, microneedling (aka dermal rolling, skin needling, fractiional microneedle resurfacing), another relatively inexpensive modality, may be used to help the surface tone and texture of the treated region blend better with the surrounding normal skin. In fact, in a recent lecture entitled, “Will Microneedling Replace Lasers?” at the 2016 American Society for Dermatologic Surgery (ASDS) annual meeting in New Orleans. a leading laser expert reported that "microneedling is already replacing fractionated lasers..." for use in treating " various scars (from acne, trauma, surgery)." For more information on any of these techniques, I suggest you check out the archives of RealSelf.com. Be sure you consult with a board certified aesthetic physician before proceeding. Best of luck. 

For this type of scar you either need to go surgical route and do scar revision and then do LED treatments, PRP And lasers to smoothen the effect.  Or do numerous subcision, filler and laser treatments. no single laser will ever improve this in one treatment.  And to get improvemen with laser you need to do subcision for sure and be aggressive (ie 3-6 weeks downtime treatment unless you want 6+ treatments to see improvement).  Best, Dr. Emer.

Hello and thank you for your question. Based on your
photograph, you may benefit from a scar revision with re-draping of your tissue.  Personally, I would not perform a z-plasty or w-plasty. 
No matter what you do, scar optimization treatment post-op is very important.  The most important aspect is to find a surgeon you are
comfortable with. I recommend that you seek consultation with a qualified
board-certified plastic surgeon who can evaluate you in person.
Best wishes and good luck.
Richard G. Reish, M.D.
Harvard-trained plastic surgeon

A z-plasty is not the right solution for this. A W-plasty or step plasty is the right way so that some of the scar can be converted to a transverse position along the relaxed skin tension lines.   Be aware that the scar will be very red for a year or more.