Originally Posted by Jellby
In LaTeX thin spaces are dealt with automatically with the babel package. You don't have to actually write the spaces before ";", "?", etc., they are automatically inserted (see [thread=19978], for example).
Did you do that with pdfTeX or XeTeX ?
Last time I used LaTeX was around some 20 years ago, so I'll definitely won't be affirmative on the matter but:
My answer to roger64 was specifically about XeTeX, which replaces babel with polyglossia. Whether a) babel and XeTeX are compatible b) polyglossia does thin spaces the way babel does, are both unclear to me. Some say Yes, others No ... and I'm not going to install the whole stuff to give it a try.
Now, if doing only latin, we might probably agree that one will get better result with pdfTeX than with anything else. Provided you're ready to go with available fonts (there's enough for various tastes, but not mine).