Generally speaking, if you use wattage to regulate your mod, you ignore voltage. A vw device varies the voltage to meet the wattage demand and you no longer care what it is. The advantage to this is that the power is constant to the coil regardless of either battery voltage or coil resistance! Cool, huh?
Vv devices let you set voltage and it remains constant. But the power delivered through the coil (heat) will vary with the resistance, so 4.5 volts on a 2.5 ohm coil will be very different than with a 1.8 coil. Not a big deal to adjust to, and many people feel that finer voltage control works best for them. But being a set it and forget it kind of guy, I usually use watts to gauge my vape experience.
There is no right or wrong, just personal preference. Whatever gives you the vape you want is the right answer for you.