Always use a readable font, sentence case and a suitable font size – at least 12pt for web and print.
Why this matters...
Sentence Case
Words can be identified by their shape. Readability is reduced with all caps because all words have a uniform rectangular shape.
Font
Unusual fonts with unnecessary flourishes can be hard to read.
Size
A small font size is more difficult to read.
Readability and legibility are key considerations for all users. Some people may have difficultly tracking along a line of text if its line height (a.k.a. leading) is too wide or too narrow. Some people need to enlarge text to read it and will not be able to access content set in a text size that is small or doesn’t scale correctly.