an inline6:
- is perfectly balanced for forces and moments, without the need for counterbalancers
- has evenly spaced exhaust pulses; aside from the smooth sound it makes, this makes it more conducive to exhaust tuning, e.g., to take advantage of scavenging
- the long engine block, head and gasket make the differences in thermal expansion between these dissimilar materials more pronounced, contributing to gasket failures
- is easier to use a turbocharger with, because the exhaust ports are all on one side


a v6:
- has a shorter, more robust crankshaft
- is easier to use a supercharger with, the Vee of the block providing a natural location to put it