WKT carries geometry only, with no names or properties. KML opens in Google Earth and Google My Maps. WKT is at home in writing a single geometry in a database or script; KML is the usual choice for places, routes and tours viewed in Google Earth.
Every format is read into plain GeoJSON features and written out from there, so coordinates, names and properties carry over wherever the target has a place for them. Each geometry in the file becomes one feature without properties; WKT in a coordinate system other than latitude and longitude is refused. Altitude and per-point timestamps are kept; a line with timestamps is written as a Google Earth track that can be played back.