I would recommend Lightworks probably as number one. It's very versatile, has a ton of features for free software, and uses a full timeline, unlike Movie Maker and some more basic versions. However, it is limited in some regards, such as the free version's render output being capped at 720P. Also (in my experiences), sometimes when editing very large videos with a plethora of special effects and many cuts and clips from different sources, if the program is running for a long time, it will glitch out and eventually crash, and can only be restarted if the PC is rebooted. Again, this is just my personal experience.
VideoPad video editor is another great piece of free editing software. I haven't used this in quite some time, but it does offer a detailed timeline and some nice special features. It is a little more cumbersome to use than Lightworks and has fewer effects, but it still does let you do the essentials such as web cam or image overlays like some YouTubers like to do.