According to Chicago Manual of Style, 17th edition
Italics can shall be used in most of cases for emphasis or make words
stand out in general, but rely primarily on sentence structure to do so.
Never italicize a whole sentence.
Boldface and underscore are considered less appropriate in formal
prose, especially in print.
FULL CAPS are only used ironically.
SMALL CAPS are used to express terms in some places. It’s
much more graceful than FULL CAPS.