After watching both 4K and 3D (select scenes) the 4K is sharper and cleaner. The colours pop thanks to HDR/WCG but I have to admit that the 3D on this looked amazing. It gives 4K a run for the money. I would say there are plenty of awesome 3D moments in this. There is so much depth and immersion on the 3D.
Although I don't watch that much 3D, it is quite sad that TV manufacturers have ditched it completely instead of working on 4K 3D.