Arri Alexa looks better overall to me.
Mark Toia delivers a magnificent monologue about why the RED 8K camera sensor is his choice for motion capture.
Want to see something amazing in ultra-ultra-ultra HD? How about this video of bladesmith Tony Swatton making a sword? It's shot on the amazing RED Weapon 8K camera. Do I need to tell you to watch this one in fullscreen?
There, I made the video small so you have to fullscreen it.