Profound vs FaceTite vs J-Plasma: Which treatment would be best to treat excess laxity?

There is no "best" treatment and often then need to be combined.  For example we often do Renuvion/Jplasma or Facetite with morpheus or fractora (better than profound in my opinion).
With significant neck sagging you would need a neck/face lift with muscle tightening (platysmaplasty). at the same time lasers (fraxel,  co2 or erbium( or microneedling RF (fractora/morpheus, intensif) can be . performed to improve the crepe skin or wrinkles.  You need a formal consultation, as the neck can be treated with a combination approach:
1. micro needling and lasers for texture
2. botox, disport or xeomin to help platysmal bands
3. intensif or fractora RF microneedling for crepe skin and lifting
4. fillers like belotero, restylane silk, juvederm volbella to improve lines and folds
5. neck/face lifting if sagging is prominent or early starting +/- platysmaplasty (muscle tightening)
6. J plasma/Renuvion, thermiRF, inmode facetite for internal tightening
7. ultherapy and thermage for external tightening
8. regular Venus legacy, exilis ultra, or inmode forma treatments with facials to maintain tightness
9. PDO novathreads or silhouette instalift cone threads for lifting and long-term collagen production
see an expert for a full evaluation and treatment plan based on your individual situation and goals.
Best, Dr. Emer.

You need an in-person consultation and evaluation. These 3 treatments you mentioned are all completely different and comparison head to head doesn't really make much sense. At 28, you probably don't need any aggressive measures. In general though, any treatment that is subdermal (under the skin) such as FaceTite or ThermiTight will give more dramatic results than superficial or completely non-invasive treatments. Make sure you see an experienced physician. Best wishes.

While all 3 should give improvements, my preference is for FaceTite. You will get much more energy into the tissues with this vs Profound. They both have feedback on temperature parameters which makes them fairly safe. All 3 require tumescent anesthesia. If you are talking about J plasm subcutaneously, my concern is that there is no feedback as to what the tissues are doing and how much energy is delivered. I would be even more concerned about using J Plasma on the superficial skin. There is 2-4 weeks of healing at least  when this method is used. I'm also concerned about complications such as scarring and pigmentation issues. FaceTite would be the best choice.