Here is some practice I made to load KMLs in Web GIS. In my case, I compared two ways of handling a KML file that contains a KML overlay tag.

Demo 1 - Using ArcGIS KMLLayer

What I like about: dead easy

What I dislike about: KMLs need to be uploaded somewhere before adding as a KMLLayer layer.

Demo 2 - Using my own KML parser

What I like about: I can just drag in my KMLs from local; more flexibility of handling KML-formatted spatial objects

What I dislike about: I have to test with loads of KMLs in order to get a robust parser