Love the supercharged V6, it's light on its feet and power delivery is instant compared to the 5.4L V8 in the C55 which felt a bit lazy.
My c55 was a bit frustrating as it use to slide everywhere in damp conditions, with 412lbft torque it desperately needed an LSD which my c32 benefits from.
My 407hp C32 is faster in a straight line than my tuned 398hp C55.
Handling and steering feel on the c55 is much better especially on mine as it had coilovers.
C32 drinks less fuel and is cheaper to insure.
Sound I personally prefer the wine and roar of the supercharged V6 over the V8 in the C55 which I found a bit too quite.
This is just my opinion, most people would probably take the c55s better build quality and reliability over the c32.