They shouldn't really matter, except for file size. They won't magically use different SVG markup. All Plain SVG does is strip away Inkscape's XML namespaces and custom attributes/elements. There's a fair number of SVG features that are poorly-supported, broken or with a number of gotchas in various renderers, however and you're kinda expected to work around those yourself.
For icons and similar you can often go back to the most basic things: Filled paths with solid colors and gradients. That should render pretty much everywhere where there's at least some SVG support.
For icons and similar you can often go back to the most basic things: Filled paths with solid colors and gradients. That should render pretty much everywhere where there's at least some SVG support.