VV V3 pros - self contained no extra battery charger needed, small and light weight
cons - only 800mah - may not last all day if you are a heavy vapor, BUT it will work as a pass through
device if you are stationary where you can plug in a usb adaptor (I do not recommend plugging into a computer), whole unit needs to be replaced if battery fails
SVD - pros - larger device will work and look better with larger atomizers ie: protank, iClear30,
rba's etc. Uses replaceable
batteries and is telescopic to adjust length based on battery chosen 18350 - 18650
cons - needs a separate battery charger (I recommend a nitecore intellicharger). Larger and heavier - not pocket friendly
hope this helps