I'm no expert on fonts, but I know the basics. The reason you haven't gotten an answer is probably that your question is so general that its difficult to answer.
On a good day, all modern fonts scale to the size selected by the application. But the reality is that some fonts generally look better in smaller sizes (I'd say light,thin,sans-serif) and some look better in larger sizes (heavier or serifs). Then there are subtle differences in the rendering software used by various applications (like browsers) that can have an impact on the appearance of the generated text.
So, overall, there's no 'best practice' other than to select a font that works well in the size(s) required.