Haha, this was actually a thread that I posted months ago, titled “To Use YafaRay or Indigo? That is the question.” What I learned from all the responses to that thread was that you have to know what is that you want and that will help you decide which render engine you choose. Essentially, what Myke just posted above me is what you need to consider.
Also, keep in mind (now this is from pure memory, sorry), biased render engines are what you need for animations and unbiased render engines are what you use for still shots/still progressions. So stick to YafaRay if you want to want raytracing for animations, otherwise, go for Luxrender if all you need is still shots. Trust me, this was well covered–it may benefit you to search up that old thread if you still need clarification—Renderman was also discussed in that thread as well.
Hope what I said helps you with your decision. Happy blendering!