There are, indeed, many choices ... and more being added almost daily. There are three factors involved in this issue: the
atomizer (either as a separate component or as part of a cartomizer), the
watts (i.e., battery voltage interacting with atomizer resistance to produce power), and
how juice is fed to the atomizer.
Feeding the Juice:
- From what I've read, bottom-fed juice feeders (the REO is one, very good, example) may do this the best, but they (at least the good ones) tend to be expensive ($125+).
- I've never tried the large tanks (e.g., MAP): many vapers rave about them, but they seem complicated and look ungainly to me. I have been unimpressed by the smaller tanks (e.g., eGo-T and Lea), although, again, they have their admirers.
- For the better part of two years, I did direct dripping on the atty coil, which rivals the bottom feeders in effectiveness and is inexpensive, but requires more frequent effort.
- At least for now, I dwell in the land of cartomizers, which, in the main, are far superior to those of the past. The good ones include the Boge, Smok Tech Dual Coil* (including the new eGo-sized version), and CE2 that Kurt mentioned, as well as IkenVape's 510 cartos, the Kr8's from Bloog (Maxx Fusion) and Smokeless Image (VOLT), Echo and Echo-e, and 801 cartos (Boge, EastMall, and IkenVape). [Also the Leo and Go-Go, but they're not compatible with anything else, so we won't get into those.] Lots of choices, eh?
* I've not yet tried Patty's Diamond Duals. Based on her comments here, add them to the list.
Atomizer: The choices used to be limited and straightforward 510 (and its cousin 306), 801, or 901 ... and in cartomizers Kr8 (that E9 stuff you can buy in malls doesn't count). Now there are new ones (e.g., the previously mentioned Leo and Go-Go) and all kinds of variations within the old, especially within 510. The threading remains the same within each model number, but (to me at least) what primarily distinguishes one atomizer from another is the
feel of the vape. For example, the vape from Smok Tech Dual Coil, Boge, and Echo-e cartomizers (all with 510 connections)
feels different ... and the vape from any of the 801's feels
really different from them. [FYI: I happen to love the 801 ... although that dual coil is giving it a run for its money.]
Watts (i.e., the power or intensity of the vape): User control of this used to be entirely with the battery
voltage: 3.2V (e.g., 510 and eGo), 3.7V (e.g., Kr8 batt, some fat batts, and mods), 5V, or 6V ... and now variable voltage. Then there was a choice in atomizer/cartomizer
resistance, but limited to either standard or "LR" (usually 1.5Ω) or "HV" (i.e., high-resistance for use on 6V mods). Now there are seemingly endless choices, especially with 510 atomizers and cartomizers. Once you find one or more attys/cartos you like, experiment to see which of the available resistance levels for them you like best on your batteries. Check out
this article for more information on atty/carto resistance and this volts/ohms/watts/amps stuff. [For example, you do
not want to use 2.0 ohms or less on a 5+V battery.]