Many eCig users feel that the two-piece design is the best overall when compared to disposables and those that have three pieces. Two-piece eCigs have just the replaceable cartridge and the battery which can be recharged. The atomizer is built directly into the cartridge so each time you replace the cartridge, you are also replacing the atomizer.
Changing the atomizer every time the cartridge is changed means that you have no worries of the atomizer malfunctioning or getting clogged. You can switch your cartridge to one of another without worrying about the flavors intermingling in the atomizer. Of course, there are disadvantages to practically everything and the main disadvantage to this type of electronic cigarette is some cartridges that have sealed atomizers make it a bit difficult to refill yourself. If you prefer to refill your cartridges as opposed to buying them prefilled, this may not be the best design option for you. You can refill cartridges that have sealed atomizers but it is a bit more difficult and many feel that it is simply not worth the trouble.
The three-piece models contain a separate cartridge and atomizer along with a rechargeable battery. In order to use the eCig you simply attach the battery to the atomizer and then attach the cartridge. The main advantage of a three-piece design is it allows you to easily refill the cartridges yourself with your chosen liquid. Those who prefer this less costly method of refilling will find that a three-piece design works best. It is much easier and more convenient to refill. If however you prefer to simply purchase cartridges that are already filled, the two-piece design will work well.
The main advantages of the three-piece design, which the two-piece design does not have, is that you have to replace the atomizer whenever you decide to change flavors. The atomizer on a three-piece design also has to be replaced at least every couple of months and this is an added expense that many eCig users simply do not want. The cartridges for the two-piece models are a bit less costly and they are much more convenient to change as opposed to refilling cartridges and replacing the atomizer at regular intervals.
eCig users will have to make up their own minds as to which design is best for them. If you prefer to fill your own cartridges then the three-piece design may simply be the best choice. There is also a notable difference in the vapor that is produced between the two models. The two-piece design normally gives you a much thicker and higher level of vapor production than three-piece models which is one reason that some users prefer them. More vapor means a better throat hit which gives you a better sensation of smoking a traditional cigarette. If you prefer more vapor, a two-piece design may be best. If vapor is not a major concern however and you prefer the lower cost of filling your own cartridges, three-piece designs may be the best choice.