Question on cleaning

[JSchni]

I have heard two ways of cleaning the engine compartment. Both start with spraying a decreasing spray but this is where they differ. One says you can spray water over everything, the other says to cover the alternator then spray.
what is the proper way to wash the compartment and does anyone have any suggestions on a decreasing spray?

 

[Chewy]

Cover any open air filter elements if you have any, otherwise, I hose, spray with Adams APC, let dwell, scrub with a boars hair brush and rinse. Repeat as necessary.

I use my Adams fire hose nozzle. I DO NOT use a pressure washer.