Here are two popular brands of 4 stroke 20 horsepower outboard motors - a 2013 Honda BF20 and the 2017 Yamaha F20C. I've had the fortune, or perhaps the misfortune, to own both so thought I'd let you know my impression of each. We've owned the BF20 for over 3 years, was purchased new, used almost daily and maintained as per the manual. It's been often, driven moderate to hard. The F20C (C stands for 'Commercial') we've had now for a month, is now broken in and is our mainstay outboard. Both engines are stock engines off the shelf.
Here's my impression.

+ BF20 is more fuel efficient than the F20C at 50% throttle; guessimate is 10-15%
+ BF20 has better low end torque however each are about the same at the upper end of the torque band. Overall I think the F20C drives our 3.5m Al dinghy faster. Note this could also be a prop pitch choice.
+ F20C runs quieter at mid throttle while the Honda is quieter at idle.
+ Our experience with the BF20 is that its very sensitive (too much so) to the quality of fuel. We've gone through 3 carburetors even though we use an external fuel filter/water separator. The F20-Commercial is advertised to be less sensitive to fuel quality.
+ We found the BF20 overall unreliable. While I've maintained it according to the ops manual and never abused it, we seem to always have numerous and varied breakdowns. Outside of regular maintenance these include: replaced carb (3x), fuel pump (2x), broken throttle cable, broken ignition cable (2x), prop seals (not a fishing line issue). The final problem, and its last stand, was unsolved after 3 outboard mechanic inspections including that of Honda. Its now for sale!

For our Honda to fail us as often as it did in 3 years was a surprise and disappointment (fiscally) and we began not to trust it when we wanted to go on longer excursions. We had heard many positive reports for the Honda from other cruisers and locals around our marina (Keppel). Perhaps ours was built on a Monday morning! On the other hand, the Yamaha is a stalwart of outboards so we are expecting a good life from it. Also noteworthy is that we have always had trouble finding Honda service centers in our international travels and had to import these parts. And we've noticed that Yamaha are much more widely represented.