Six devices/brands come immediately to mind, all with their own particular strengths.
Provari V2
Legendary reliablilty, build quality, design, performance, and all-around greatness. Made in the US of A, built like a tank. The Cadillac of APV's. Last I checked, $159 and up without batteries. Want gold-plated? You can get it. I'll be buying a silver one with blue LED if and when they make some more.
Smoktech VMax
The new kid on the block. Great performance, uses two x 3.7V AW IMR (safe chemistry) batteries giving it 7.4-8.4V to work with, three-digit LED, heroic 5-amp limit, unproven. Around $100 some places with two batteries. Can cost as much as $128 without batteries. I'm vaping on mine as we speak. Love it. Ignore the hype about the tremendous dangers of "stacked" batteries, but only if you use IMR (Lithium-manganese) batteries, which as I understand it, will not "explode". *
Joyetech Twist
Just came out recently. Variable voltage at a very low price. VV between 3.2 to 4.8 volts in the eGo form factor. Some call it a "game changer", and I tend to agree. It is what it is; it is not a replacement for a big-battery VV APV, it's a great little "pocket VV (A)PV". Works best IMO, and very, very well, with a 2.0 - 2.5ohm single coil - like inside a DCT tank, or whatever attachment floats your boat. Available in black, chrome, blue, pink, white. 650, 900, and 1000mah, although not in all combinations. $25-30. Great reviews. I just got 30 of them for starting people out on.
http://www.e-cigarette-forum.com/fo...s-discussion/290152-joyetech-ego-c-twist.html
Reo VV
I have never "plonked", but I plan on it. This particular line of bottom-feeders has an avid following that seems to me to be well-deserved. Check 'em all out.
Lava/Apollo/many re-brands
Also has a large group of enthusiastic supporters. Comes in many different sizes and variants, all of which seem to work very well, for a very good price, starting at around $50 as I hear it.
Buzz Pro 2
Legendary ruggedness and reliability. Have never heard anything bad about them.
*****
IMR batteries are "unprotected" batteries, which sounds bad, but IMO isn't. "Protected" batteries typically use an integrated; well, IC - (Integrated Circuit) - to regulate the flow of electricity into and out of them under normal operating conditions. That circuit is typically designed to keep them from being overcharged or discharged too low (which severely damages most or all lithium-based batteries) - but it does nothing whatsoever to mitigate the consequences of an internal short, in which the battery's chemistry dictates the outcome. In the case of an internal short, you're better off, again IMO, with an "unprotected" battery that will not "explode", but will instead get increasingly hot, giving you ample time to drop the PV - than with a "protected" battery that can quickly release energy in a much more violent fashion. I believe that the more 'explosive" types include ICR (lithium cobalt) and LiPo (lithium polymer). The "safer" types include LiFePO4 IIRC.
In case of an external short (like what would happen if you attached a heavy wire to each end of the battery), an IMR battery would again become increasingly hotter - up to maybe 450-500 F. - but would not "explode".
Callies Kustoms IMR Battery and AW short circuit observations - YouTube
Callie's Customs IMR short-circuit tests - AW IMR
As I understand it, a "protected" battery that suffers and external short would not even get hot, since the IC would act like a circuit breaker, perhaps self-destructing in the process, but stopping the flow of electricity. If I'm wrong about that, I'm relatively sure I'll be corrected.
An "unprotected" battery will have to rely on the device it's being used in, and the charger it's being charged on, to keep it from being over-charged (kept at 4.2 volts or so) or discharged below about 3 volts. The nominal voltage on these types of batteries is usually 3.7.
***
In closing: variable voltage (or variable wattage) is really the only way to maximize your vape on a wide variety of attachments, especially ones with varying resistances. Ohm's Law cannot be gotten around.
Speaking of variable wattage, I left out the Darwin, which in its own awesome way could arguably be called the most advanced (quasi-mass-production) APV on the planet. I want one bad. Select the wattage you want coil or coils to get/consume/create, and it makes it happen based on what it knows their resistance to be. It doesn't get much slicker than that. I'm looking forward to a single APV that will do both VV and VW. Please refrain from telling me that it can't be done, as I'm running out of forums.
