There are sub ohm coils and non sub ohm coils.
Sub-Ohm is any kind of coil for any device that has a resistance of less than 1.0 and non would be anything greater. The lower the resistance of the coil, the more power it will demand and will allow for bigger clouds and more vape. This means that you will also require a device that can push that kind of power.
Sub-ohm coils are popular among the “cloud chasing” community. 0.2 is usually as low as you can go safely with any kind of battery, but building it lower than that will yield bigger clouds.
non-Sub-ohm coils are popular among everyone else. They typically revolve around either 1.2 or 1.5 ohms. They require less power to use and these are favored by people who want to vape all day.
Personally I enjoy a middle-ground. I like the sub-ohm coils because i can get a huge mouthful of vape and get the nicotine rush when i need it, but vaping too high also requires me to inhale or ‘pull’ on my device for a longer amount of time, which also drains the battery. I use either a 0.4 or a 0.7 ohm coil because, again, i feel like this is a balanced middle ground.
Most starter kits nowadays all come with one sub-ohm coil and one either higher sub-ohm or one not. I am using the cleito tank by Alantis and it comes with a 0.4 and and 0.2 ohm coil. However the eleaf mini comes with 1.2 ohm coils because it is a smaller stealth device and is meant for discreet vaping.
It’s really just personal preference. When i was big into the cloud-chasing community, i built my own coils as low as 0.02 ohms (very dangerous if you don’t know what you’re doing electrically, i do not recommend) to blow the biggest clouds and I also built coils as high as 1.5 or 1.8 because I wanted a mellow all-day-vape that wouldn’t drain my battery.
If you want to look at it mathematically (which i won’t dive into in this answer) you can look at ohms law. The lower the resistance the more power you’ll require and the quicker you’ll drain your battery and vice versa.