Assuming Windows 10 (or 8/8.1), I personally create a backup of the factory reset as per the laptop manufacturer's instructions. The I create a bootable USB of the accurate version of the OS and clean install the OS with the official ISO's from MS.
Removes all bloatware etc, as it's the 'base' OS. The OS will also activate automatically too, so no need to re-enter the product key (again, assuming W10 or W8/8.1)