I would imagine the straight 6 would be the smoother engine as fitted to BMW, Jaguar, Nissan, Austin Healey and how can we forget Aston Martin! Better engine balancing and pairing of cylinders.
Nissan chose the straight six for the Skyline as it was better balanced and could rev higher than the V configuration engines. Interestingly a V8 was also considered in the Skyline development
My V6 revs to 7000rpms and that's just before the limiter. Revs beautifully. Sits on the arse of my step brothers BMW 330Ci straight 6 Very smooth engine but the power delivery is like a turbo due to the VIS system on the inlet. Fully opens at 3500 rpms and literally feels like a turbo kicking in