Hi there
Where to start there, I personally use like Octane, Redshift, Cycles(E-Cycles) and Poser SuperFly or Corona Renderer amd in some cases I use V-RAY Next in 3DS Max
I don't render in DS at all, not sure why, but I just hate DS UI, usually I export everything from DS and start to render in Blender or Poser or 3DS Max or Cinema4D, I tried several times IRAY with which I'm still unimpressed
When it comes to speed, Redshift hands down is fastest renderer, E-Cycles is in my view second, Octane third, Cycles/V-RAY Next is 4th, IRAY/SuperFly is 5th and Corona is last but you need take to account, Corona is CPU based renderer, bit still is quite good and usually on 5930k render at 1440p takes me 45 minutes to 1 hour
I tried Arnold Renderer and I quite like it, just is way to slow if you are comparing Arnold Renderer to other render engines
If you are going for realistic look then shaders will play big part of the render, lighting as well and then props, I usually pay more attention to props and textures and usually I prefer to use non DS or Poser props like environments etc, usually I use Evermotion or any other good props which are highly detailed or are just better but there are cases where I rather use props from Poser or DS which looks OK just I rework materials, use different textures and add bump maps etc
With skin shaders that's difficult to recommend, in Poser I use EZSkin which does great job for me, bit still there are few tweaks needed to have nice materials, in Octane I use Mix material for skin which does work but still not very happy with skin, Redshift that's different and there I still can't get good looking skin because of DS or Poser textures are not the best and you are really need to edit them in Photoshop but they're usable just they don't look good, but that's my view on this, Blender E-Cycles or Cycles to you can try few free plugins like mcjTeleBlender which I use and works for me there, Corona Renderer its quite easy to use and usually I can get out of box nice renders and skin SSS is quite nice there