Actually an inline six is just about the best engine possible in terms of inherent balance short of a V-12. They don't even need counterweights, while a V-8 is pretty good it's not perfect and also the exhaust doesn't split as nicely as a six does (which is why a six SOUNDS smoother and the V-8 has that typical "lope," unless it has a special exhaust system that has even-fire exhaust headers, which would necessitate feeding each pipe from a combination of cylinders of both banks)
nate