Probably the most off the wall choice in this thread, but I say HP Scan and Capture: https://www.microsoft.com/en-us/store/apps/hp-scan-and-captu...

It's a Metro app for Windows 8.1 and up to scan with HP scanners. I love it because it just works, which has never been my experience with scanning[0]. You press a button, it scans whatever's on the tray. You can tweak resolution if you want. And at the end you save it as a PDF. Simplicity is something that I think tends to be forgotten when it comes to GUI software.

[0] Except for a commercial scanner I used once where you put in your email address at the beginning and for every scanned page it sent you an email with an attached PDF. Although that has its own issues.