NES:Video Output Notes
Being a product of its time, the original Famicom only has RF out as its sole video output. It is also rather subpar being susceptible to interference and plagued with jailbars. The jailbar issue is largely due to a combination of poor board routing and insufficient decoupling between the 5V and ground rails. Thankfully, the Famicom can be modified for composite video and even RGB with an NESRGB kit.
NES front loader
The Twin Famicom was the first version of the Famicom hardware to offer composite video output, which made it a more attractive option for consumers in addition to its built-in Famicom Disk System. Like the NES, both video and mono audio are available through RCA jacks, which are mounted at the rear. For TVs without composite video input, Sharp offered an external RF modulator (model number AN-58C) which connected to the video jack and an 8-pin DIN connector which provided audio and 5V.
Sharp used a different circuit for the PPU's video signal compared to the NES, which arguably provides slightly superior video quality over the NES or AV Famicom.
The Famicom Titler, released by Sharp in 1989, is very unusual in that it is the only consumer-level version of the NES/Famicom hardware to use an RGB PPU, specifically the RC2C05-99 chip. Despite this, the Titler does not actually have RGB output (although it is rather trivial to add). However, the Titler does have S-video out, making it the only NES/Famicom system to have anything better than composite video. Due to its use of an RGB PPU, the color palette on the Titler is significantly different than a system with a standard PPU and certain games are incompatible due to how the RGB PPU handles color emphasis bits.
NES top loader
Towards the end of 1993, Nintendo introduced a complete redesign of the NES which featured a smaller top loading design. While the redesign proved to be much more reliable than the original front loading design, it unfortunately did away with the composite video and audio jacks in favor of RF output only. Since the top loader was a budget console, this in itself is not too surprising, but the top loader suffers from the same jailbar and video interference issues as the original Famicom did. This is once again due to poor PCB routing and insufficient filtering between 5V and ground.
Nintendo seemed to acknowledge the problem, as a board revision exists which attempted to improve the video quality and was supposedly made available to customers who complained to Nintendo about the image quality from their top loader. At some point, Nintendo took this a step further and introduced a top loader revision which featured the same multiout port as the SNES. This is the only top loader revision to have composite video and is extremely rare, with only a handful of examples popping up over the years.
Thankfully, many of the top loader's video quality issues can be fixed with an AV mod. Performed correctly, an AV mod should eliminate most of the jailbars and provide a picture comparable to a front loading NES's video output. The top loader can also be modified with an NESRGB or Hi-Def NES kit to provide even more high quality video output options, such as RGB (for the former) and HDMI (for the latter).