For myself, being not a real fanatic about some of the finer details, and put off by too many sharpening artifacts, I tend to do whatever is the minimum required for the purpose. Especially when you can't tell what a forum software will do, or how a person's own system will process things, I do little or no sharpening for posts, which gets some critics upset. For JPG images on forums, I have generally just used the freeware "Faststone Image Viewer," which has a decent unsharp mask. I downsize first, and then add just enough to sharpen up the edges - in Faststone that's usually a setting of between 15 and 20. Above about 18 edges start to glow a little.
Here's a quick and dirty sample - a day lily shot several years ago with a D3200 and an old 85/1.8, exposure not metered and now forgotten. The image is not killer sharp to start with. The original NEF is downsized in Faststone without other processing, and the right hand is the same downsize with 18% sharpening. That's about as far as I would generally go. At some point you need to decide whether sharpening will make a picture better in its own right, or whether it's a miss from the start (no judgment required on this one, which was really just a lens test).