As I have written above, there are so many customisations and reinventions of atomizers over the last few years, it's near impossible to keep track of all of them. Amongst all the parts of an e-cig, it is definitely the most commonly replaced. In a way it's like a cigarette brand, people tend to try out atomizers until they find the type that best suits them. In this sense, it's hard to get a solid opinion on which kind is best. You'll have to try out a few until you find one that you like best, may it be because of its quality, the vape it produces or how it works overall with your unit.
For beginners, it should be noted that sometimes, stores refer to “atomizer” as the first ever mode of atomizer made available. Some of the other terminologies for it are tankomizers 510s, dual coils, clearomizers, horizontal coils, cartomizers, etc. You might also encounter it as a brand term, so be wary of that.
To have a better understanding of how atomizer works and what it does for your e-cig, let us first look at “what” makes it work. Essentially, its most important piece is the “nichrome” (a coiled piece of wire). It is wound by a wick (it resembles a twine or string). The e-cig basically keeps this wick very wet, so when the battery fries it the coil heats up which in turn vaporises the liquid/juice. This is the part of the process where the atomizer comes in – it keeps the wick wet.
What you're looking at above is an early model e-cig that shows the parts we just discussed. It's the best way to understand how all these parts work together to produce the vapor we use as substitute for cigarette smoke. As you can see, there's a battery, an atomizer, as well as the parts within the atomizer.
Within the atomizer is the coil wound around a wick. It's the coil that heats up when the battery is fired up. Inside the cartridge a fluff or wadding that's saturated with the juice or e-liquid. This wadding should be thick enough to keep the liquid in place. Once the cartridge is nserted into the atomizer, the wadding should touch off the mesh-like material made of metal – this is referred to as the bridge. The bridge works to draw the juice or e-liquid to the wick and keep it saturated.
Once you fire up the battery, the juice in the wick heats up, creating a liquid to gas chemical reaction that produces the vapor that the user inhales though the mouth piece. Please check the picture again, and this time look at the red and green arrows. The green arrows illustrate the e-liquid being drawn onto the wick and bridge. The red arrows on the otherhand shows the vapor going through the cartridge and out to the e-cig's mouth piece..
This original e-cig system, however, turns out to be ineffective. A lot of e-cig owners started to remove the cartridge and opted to directly drip the e-liquid down to the bridge itself (later on called as “dripping”). Because it became so common, someone thought of creating “drip tips”, which is basically a mouth piece with a hole where uses can drip the e-cig juice through. This removes the need for repeatedly detaching and reattaching the cartridge every time the user needs to drip e-liquid on the bridge.
Later on, a trend of removing the bridge altogether also picked up. This is so e-cig users can directly drip juice down onto the coil. Today you can even buy an e-cig with an atomizer that no longer has a bridge. Examples of this are the 306, io6, HH.357 atomizers, which are specifically designed for the “dripping style”. People who like to experiment on and taste various type of e-liquids prefer these as they only need to “drip” a few of the solution to give a particular juice variant/flavor a try.
Here are some YouTube videos of people manually taking the wadding out from the cartridge. They do this so they can replace it with a material made out of teabags. It turns out that these do a better job than the wadding:
The earlier types of atomizers (like the ones shown in the video) come in small, medium and large variants. Like most e-cig and e-cig parts, they are being made by factories in China. They all do a lot of “imitating” or “copying” of each other's innovations, and sometimes they even copy personal mods or customisations.
The e-cig models, like the 901, 801, and (the more popular) 510, are actually name of the e-cig's threading. This usually is referring to the type of threads a battery or atomizer has so you can tell if you have a battery which fits a particular atomizer and vice versa. Since models have different sizes, along with different battery and atomizer sizes, they needed to have a standard threading so they can screw and connect with each other. Over time, the threading names became the actually names for the earlier e-cig models.
Today, the 510s have become so popular and common that almost all batteries and atomizers have a 510 threading by default. Adapters that enable e-cig owners to fit any kind of atomizer to any battery have been made available in the market however.