These 3 cars are in the range of $300k (brand new) and 2,000 cc. Any idea which one is better?

Audi is usualy more reliable at least for American models with BMW right behind it. Mercedes is definitely way behind on reliability. as for build quality i would say its Audi then MB then BMW and for driving dynamics and handling i would say BMW then Audi then MB but i cant comment on the exact models as we only have the A3 in the US right now.