THE THEORY
It depends on quite a few factors.
The Liquid itself
The wicking style/material/action.
The draw style and air flow.
The number of coils in the build.
SINGLE COILS:
Draw Style:
First consider how you best like to take draws. Do you like a very short and fast draw right to the lungs? A slow draw into the mouth, and then into the lungs? Do you want a 'hot' or 'cool' vape? If you like a longer, slower draw style, then higher resistance stuff is the way to go...as you can set your PV for lower settings to balance heat with what your wicks can deliver. If you like a really short puff, or expect really fast reaction times for the coil to go from ambient to really hot...then you might like lower resistance stuff.
Range - The true advantage of a VV/VW device.
If you have a VV or VW device and a good high drain battery, then you can achieve the most 'range' with a coil from 2 Ohms to 3 Ohms. By 'range' I mean you can experience cool coils, or quite hot ones, with a lot of resolution between. Something around 2.5ish Ohms would let you experience the low range as well as the higher range. In contrast, a really low resistance coil might not allow anything less than 10 watts, even with the lowest VV/VW settings your mod can achieve.
Now consider the 1.2 Ohm option. If this is a 'single coil' atomizer, then the coolest/lowest power you're going to be able to achieve with most VV/VW devices (assuming a low bucked voltage of around 3.5 volts) will be around 10 watts. That's pretty hot for a single coil, so the wicking action and air-flow needs to be very good! The advantage to such an option, is that you could get really fast/hot vapes up to the maximum current limit of your APV (advanced personal vaporizer)
PWM and low resistance stuff
Some VW (variable wattage) APVs will use PWM (Pulse width modulation) and may be able to simulate going below the minimum bucking voltage. It might sound like a rattle snake up next to your ear instead of giving a steady hiss, and vape quality might be excellent, or it might be awful. In theory...it should be good, but results will vary depending on how the atomizer is built, and the liquids you use. This works by 'pulsing' the signals through the coil at a slower rate than it would otherwise. Even so, you'll probably experience a 'smoother' vape with higher resistance coils around 2.5ish Ohms.
MULTIPLE COILS:
Dual coils change the equation somewhat. With these you'll most likely want the lowest resistance that your mod can safely handle, plus a bit of head room to prevent 'error messages'. These spread the total wattage over more than one coil. A 1.5 Ohm dual coil system will usually be made from two 3 Ohm coils. Such a build would be unlikely to burn/scorch since it's spreading the watts over two high resistance coils. It would however, offer a LOT of vapor due to more coil surface touching wick. It will also consume a good deal more e-liquid. It would also draw close to 3 amps at the lowest setting of 5 watts (2.5w per coil @ 3.5v), and quite a bit MORE with higher settings.
If you try dual coil cartos, buy in small quantities to test first! Do spring for high quality IMR high drain batteries. If you're building your own...experiment with caution. Learn to use an Ohm's law calculator, multi-meter, etc, and keep the current in the safe range of your PV and Batteries.
To get 10 or more watts to 'both coils' will require a demanding setup-up that stresses batteries a good deal, or requires a different battery platform. I.E. A HV set-up (5 Volt rigs are less common these days, but they do work well with dual coil cartomizers), a DNA 20 mod, Helixed DNA 12 mod, or some VV mod that has an HV mode (stacked batteries), or doesn't limit the current so soon (most will limit current to 5 or less amps), or sub-ohm set-ups from carefully selected super high drain batteries.
SUMMARY
With single coils and a VW/VV APV you'll get the most adjustable range by using a 2.5ish Ohm coil.
Low End: Bucked - 3.5v - 1.4a - 4.9w
High End: Boosted - 5.5v - 2.2a - 12w
That is the 'full range' of the most common VW/VV APV devices out there these days.
If you go with lower resistance coils, then you start to lose the lower settings...even tho' you might set the dial at the lowest setting, you'll actually get something higher, or less predictable (in the case of some less expensive PWM units). The benefit to going with lower resistance would be really quick reaction time on the coil getting really hot, really fast.
With dual coils on an APV, 1.5 Ohms is a good place to start. 1.2 'might work' when new on most of the VW apvs on the market today, but is prone to current limiting errors as the coil ages and bounces around in resistance. If 1.5 Ohms is the low limit of your APV, then go for something a little higher than that...like 1.8, and so forth.
