How would you compare sclerotherapy to VeinWave, VanGogh and Ellman micro RF? State of-the-art might not be the same as gold standard.

Spider Vein Therapy. All of the treatment you are referrring to can be successfully utilized to treat small spider veins. Larger veins tend not to respond well to most of those treatment methods. Sclerotherapy can treat a larger number of vein in a shorter period of time, so is more cost effective for most leg vein therapy. The other methods you listed are also useful on spider veins of the face, nose, and ankles/feet.
Some differences. Sclerotherapy is the direct injection of a solution into a vein to dissolve it. It does require needle injections but it also can cover a larger area per injection. Veinwave, veingogh and ellman microneedle rf all are similar in that they work by thermocoagulation (ohmic thermolysis) of the treated vein and they cover small areas at a time and the treatment is tedious. All treatments work.
Treatment. this is a very good question and the answer is it depends upon the size of the vein being treated, as well as the location. For spider veins of the lower extremities most are treated with sclerotherapy, with possible use of either vein gogh or vein wave for treatment of smaller size spider veins. For spider veins of the face and nose vein gogh or vein wave to better.
They all work well. Any difference in results between them would depend on the experience of the practitioner and not on the technology. All have minor discomfort associated with their use and all can cause a little temporary redness and bruising. All of them work in the right hands.