CharRam.S19 is a font i found in an Application Note

Font.S19 was extracted from the TENBUG 2.1 Rom. 

They are very simular. Only a few slight differences. Use which ever you like best.

Tenbug has a font built in and loads it when started, so no need for a default font, if you use tenbug.

GFONT.S19 was extracted from the Graphics Server.

Gfont is quite different.

Starting with Version 1.0.7, you may load a font at anytime by using File->Load Memory
 (WARNING - the font MUST be oreg'ed at the Character Gen Ram address.)
 The font file can contain the Character Attr Ram as well.