I've had decent results with the scan feature built in to Google Drive and better results with Genius Scan.

AFAIK the free version limits your ability to export or share the files as easily, but you can still save it to your phone and then attach it to an e-mail, upload to Drive, etc. after saving.

The free version doesn't watermark stuff and if you choose to pay for the app it's a one-time payment rather than a mandatory subscription. It doesn't have as many PDF-editing features as CamScanner, though.