Depends on a lot of things, actually:
Type of juice - PG or VG, where you got it from, what's in it, etc. Sometimes it doesn't vary a lot, sometimes it varies a whole bunch. Some liquid is more viscous, some is runnier. It can and does affect the amount of vapor. (See some of Teraphon's
reviews in the video section for more detail on that).
Power source - Most e-cig batteries run at around 3.7 volts, but some users have cranked theirs up to 4.2, 5, even 6 (though I wouldn't suggest it). Items like the Screwdriver, the Prodigy (based on the specs) and even a USB passthrough make a difference. Also making a difference is a manual vs automatic switch . . . you can get more vapor off a manual switch 510 than an automatic 510 simply based on the fact that you can leave it turned on longer. Mind you, it drains the battery faster . . .
Atomizer - This is probably the one you're most interested in. People have contended that a stock penstyle 801 is a vapor machine, but other people contend you can get as much from a 901. It really depends on perspective.
My best advice is to go to the Video
reviews section and look over some of the items demonstrated firsthand. Some people even use rating systems. You'll get a wider idea of how the different models operate and what kind of vapor production you'll get.
Hope that helps . . .
