Uppercase within HTML tag vs CSS text-transform

It's not a question of which would load faster even though the upper case would "load faster" than loading the extra bytes from the css.

In my opinion, there is a question of accessibility involved in that matter.

You should write the text as it is supposed to be written for a vocal reader to read it (for blind people).

Morevover, I would personnaly write it with the text-transform as it's easy to change if you have a lot of h3 in your website and you don't want to write them all over again if you change the way your h3s look.

There is a difference in document content, “MY TEXT HERE” versus “My text here” (just styled to be rendered in all uppercase). This matters in non-CSS rendering situations, in scripting, and other automated processing. Most search engines seem to dealt with texts in a case-insignificant manner, but this is not guaranteed and may change, at least in some situations. When text is copied and pasted from an HTML document, all styling is often lost so that you only get the content.

Any difference in speed on loading is most probably immaterial, but obviously the version that has the desired spelling in the content is faster than one that needs a style sheet rule to be loaded and applied.

Logically speaking, writing it uppercase directly in the HTML source would save the browser the trouble of rendering the style rule and applying a transform to the text.

But the difference of the page load speed would be irrelevant, and not noticed...