Depends on what Atrium. If closed, it's very different than open. Personally, I prefer the AC more frequently than VC, but when I do listen to the VC I always enjoy it. I'd also argue that the AC is more thick and warm than VC by a mile. VC is faster and a bit "thinner" (I am guessing due to the Atrium Damping system being more recent, VC drivers being Vapor Deposed Beryllium vs. Atrium drivers being Biocellulose). They are both great, it depends what you are going for.
VC = fast, fast, fast, with accuracy and precision.
AC= immersive, immersive, immersive, with some magic fairy dust sprinkled in the cups. It's like if Caldera and VC had a baby. Slams hard while still being accurate.