RGB is the single best video output option. RGB comes in many forms, like how 240p and 480i RGB typically comes out of a SCART connector or a Japanese 21-pin connector and how analog 480p and higher come out of a VGA connector. HDMI usually uses a digital form of RGB and displays 480p and higher. All mainstream video game consoles after the NES, besides the N64, NTSC GameCube, and NTSC Wii output some form of RGB. The NES, N64, Atari 2600, and NTSC Wii can be modded to use RGB, and the NTSC GameCube can theoretically be modded for RGB, but nobody has RGB modded one yet. However, mmmonkey has provided a guide on modding a component cable to output RGB on the GameCube.
If you are interested in RGB, here’s a bunch of information you need to know. Sync is a signal used to tell the television or monitor all the information it needs to know, and there are many types of sync. Sync-on-composite is exactly what the name implies. Same with sync-on-luma and sync-on-green. Composite sync is not the same as sync-on-composite as composite sync is separated from any video signal, and horizontal and vertical sync are basically composite sync separated into two sync signals.