I don’t know a ton about foreign motors other than surface level stuff like the 2JZ, Wankel, etc. so please forgive my ignorance outside of US motors.
However, in my eyes, it doesn’t get better than the simplicity and easily available power of the SBC, BBC, and 6BT. What are your all time favorites and why?
Mercedes 300SL engine.
In the 1950’s it made 240 horsepower out of 3 liters which was far ahead of other engines in the period.
When other engines would overheat from highway cruising, it held up to hard racing without overheating. The cooling system is so overbuilt that owners will block off an oil cooler because you have to drive the car so hard to even get it to the operating temperature.
Instead of using carburetors like almost every other car in period, it pressurized fuel to over 500 psi and injected it directly into the combustion chamber.
On top of pushing the limits of power and technology the engine is dead nuts reliable, even by modern standards of reliability.