First you should know exactly what a vape coil is, and why it is an important component for your e-cigarette or MOD. A coil is usually referred to as an atomizer head or atomizer coil, which is the portion of the cartomizer/clearomizer (the clear tank piece) that makes contact with the battery on one side and on the other side the e-liquid. This vaporizes the liquid into a vapor which then you would inhale.
The Pro's and Con's of Top and Bottom Coils
Both of these coil pieces have pro's and con's to them, and here it will be listed out so you can make an educated decision based on your wants and needs in a vape.
With a top coil design you can achieve a warmer vapor due to the coil being closer to the mouth piece, can easily be filled from the top which most people find to be easier, and low propensity for leakage. The con's of this design is frequent dry hitting, poor wicking, poor flavor production, and it must be tilted and swirled so the wick can keep wet.
The bottom coil has very similar amount of pro's but tend to have a few more con's than the top coil. The pro's to this design are really simple, they are easy to fill, have consistent wicking, and superb vapor production as opposed to the top coil. These bottom coils may make gurgling and hissing noises on the draw. These coils can leak if the seals are not sitting well or the wick is not used enough. They also drip a little from the mouthpiece when the bottom is removed for refilling the e-liquid. Sometimes they even need a little wick adjustment and that can be a tad annoying for some. As a bonus con, they can produce an airy draw.
As shown, both of these types of coils can provide excellent qualities for your vape, while on the other hand have their own unique drawbacks. Hopefully this list has information that can be put to use for the best product choice you can find for your wants and needs in a vape.