Format List

About: Download YouTube Videos as MP4
My slight rewrite:

var FORMAT_LABEL={'5':'FLV 240p','18':'MP4 360p','22':'MP4 720p','34':'FLV 360p','35':'FLV 480p','37':'MP4 1080p','38':'MP4 2160p','43':'WebM 360p','44':'WebM 480p','45':'WebM 720p','46':'WebM 1080p','135':'MP4 480p - no audio','137':'MP4 1080p - no audio','138':'MP4 2160p - no audio','139':'M4A 48kbps - audio','140':'M4A 128kbps - audio','141':'M4A 256kbps - audio','264':'MP4 1440p - no audio','266':'MP4 2160p - no audio','298':'MP4 720p60 - no audio','299':'MP4 1080p60 - no audio'};
var FORMAT_TYPE={'5':'flv','18':'mp4','22':'mp4','34':'flv','35':'flv','37':'mp4','38':'mp4','43':'webm','44':'webm','45':'webm','46':'webm','135':'mp4','137':'mp4','138':'mp4','139':'m4a','140':'m4a','141':'m4a','264':'mp4','266':'mp4','298':'mp4','299':'mp4'};
var FORMAT_ORDER=['38','37','22','18','46','45','44','43','35','34','5','141','140','139','299','298','266','264','138','137','135'];
var FORMAT_RULE={'flv':'all','mp4':'all','webm':'all','m4a':'all'};
// all=display all versions, max=only highest quality version, none=no version
// the default settings show all MP4 videos, the highest quality FLV and no WebM

Just paste in, replacing the code between "(function () {" and "var BUTTON_TEXT"

This displays all available download formats, first with audio and video, then only audio, then only video. Within these, it's MP4, then webm, m4a, and flv. And within those, highest quality to lowest. Thus the highest quality of the most common format will always be listed first.