Take an image that you have processes as the reference standard, with some edge detail and some smooth areas. A portrait is ideal, and ensure that you have applied no sharpening.
Make three more versions, each with a different degree of sharpening, make sure that the weakest of the three is quite close in on-screen appearance to the unsharpened original and that the strongest is noticeably aggressive.
Print all four at full size and with neutral lighting next to the computer screen compare these with the 100% magnified version online. Write down the differences and which is most appropriate to my taste.
1) No sharpening
2) Sharpening at 35%
3) Sharpening at 80%
4) Sharpening at 150%
When comparing the images, its easy to see that with over sharpening comes increased image noise and at 150% when viewed at full size, this is very noticeable and I feel degrades the image. Personally I prefer no sharpening or at the lower end.
My preferred image- no sharpening