if you want to use refractions and caustics or any material setting involving complex rendering modes, i would recoment yafray as it is amazingly simple to use.  however, there are amazingly few tutorials for learning how to use caustics and the few that there are are outdated confusing.  i am trying to find the time this summer to write some basic tutorials on caustics and liquids based on what knowledge i have gathered or figured out during the year.  caustics however was the most elusive of all rendering methods