Furnace , Hexing pands and zodiac ring are best for cube for WW barb.
I do not think they are the best personally, but it is effective.The nice thing is that the cube is not a cookie cutter object, there really is no "BEST" way to use it, because the best depends on your current gear and rolls. Sometimes it is more effective to throw the RoRG on it if you have a very well rolled unity and coe, or maybe it is best to use Zodiac (though it is overrated quite a bit now that overall RG damage has been lowered substantially.)
As of now, there is countless variations on the cube that actually make a huge impact. Even something like Scourge or Ashbringer on your weapon show insane overall results through the Rift, as you need to remember, RG's health has been drastically lowered, and the progress has been changed so that it takes almost 90% longer to get to the RG's. Clearing density has become as much if not more important than killing the RG itself, opening the window for many new items to be at the top level of effectiveness.