Lightshot. I use it regularly. It allows more functionality after the Print Scr button is pressed, such as uploading to the Lightshot site itself, copying to the clipboard, Searching for the selected area of the screen on Google Image Search, saving as a .JPG file, and more. I will say that it lacks certain functionalities that a paid tool, ShareX, has. However, Lightshot is free and gives quite a bit that other free alternatives do not.