They last according to how heavily you vape. I do about 10-12ml/day.
So I go through 3 3ml tank fulls a day, plus what I drip.
For ease of use, an Acorn tank with a short CE2 is very sweet. The ce2's last a couple days for me(about 30 ml) before I clean them and re-use. The carto tanks last longer if the tank is topped off occasionally. They stay moist and dont dry out for the burnt taste that usually kills them.
CE2's give a much more pure taste.
The Acorn tank has a screw off top so you dont have to use a syringe. If I pull the top tube up above the ce2, I can even drip the juice into it without removing the top. NO other tank offers this convenience. Carto tanks all have to be filled with a syringe or side port. Side ports can only be filled so high. But, a carto tank can USUALLY sit on its side without leaking. A CE2 tank must stay upright or juice will run down the air hole.
You have to weigh what your willing to put up with, for what you like best as far as hassle free goes. Nothing is as easy as pulling a cig out of a box and lighting up, but a good PV paired with the right tank comes very close. Its a lot of trial and error at the beginning, but once you get your own rhythm going its a breeze.
CE2s wick perfectly when the top cylinder is up over the coil. If its too low, it prevents the liquid from getting to the coil.
The higher the resistance of your carto/ce2, the longer your battery unit will last you.
PS both Carto and CE2 tanks are very reasonable and good quality at Parkes Vaping.
How long do they last you, and do they wick well?