Not sure what size or year motor you're thinking but boat test.com has tested a lot of the newer motors against each other relative to noise, fuel economy, weight, etc...
As far as my experience goes -
I had a friend that had the old 85hp Johnson on a 17 Montauk(remember that package from the late 70's) That motor took unbelievable abuse, and still fired up the next day. After yrs of knowing only 2 speeds I heard it needed the reed valves replaced, that was it.
My 200hp Merc 93' was a great running and smooth motor. Never a problem.
My Dad has a 07'(i think) Honda 200hp 4 stroke. Smooth, quiet with decent power However, the fresh water flush only hits one bank of cylinders, so in salt water the thermostat on the other bank of cylinders gets so corroded it fails/ overheats and has to be replaced apparently about once a yr.