The best Windows 10 tweak I've installed: Windows 7. ?
Actually, I used to tweak a lot of things, but MS has backed off on pushing their bloatware and updating whenever they want, so there's really only one thing I would highly recommend (if you have more than one hard drive) and that's to map all the Library folders (Music, Video, Pictures, Documents) to a non-OS hard drive. All you need to do is right-click on the folder from File Explorer, select Properties and then the Location tab.