As I said IMO Kawasaki and Honda are the engine to go with, and you are right it is a personal opinion. It's also my opinion that right now Kawasaki and Kohler own the market with mower engines.
Kawasaki and Honda only dabble with engines.
B&S produced 9.5 million engines in 2012.
They produce 70% of lawn and garden engines worldwide.
The "sprint" engine model 9/10 has now ended production due to not complying with emissions.
Since 1955 they have made approx 160million of that engine.
If everything was powered by the "Vanguard" range of engine then you probably wouldnt use anything else.
In 15 years of selling them I have done one warranty and that was due to engine being run in an enclosed area.
Downfall is it can be expensive so manufacturers go for a cheaper option which means quality is low.