How are you priming the cartos? Can you describe how you're priming in as close to exact detail as possible? Carto tanks, in my opinion, do deliver superior flavor and vapor production, and most important, a consistent hit. But they do, however, have a minor learning curve. Newer users tackling carto tanks usually get discouraged before they learn to properly prime the cartomizer.
It's not difficult to learn at all. I'm paging Baditude here.
Read his blogs. The best way I can describe how to prime a carto for a tank is to drip 10-15 drops into the polyfill slowly, holding the carto at an angle, and avoiding the center air hole. Rotate the carto with each drop, and give each drop a second or two to soak in. After ten to fifteen drops, or whenever the liquid looks like it's slightly pooling up, flick it HARD like a thermometer. Continue this process until after a flick you see juice coming out of the little hole at the bottom of the carto. I used to count drops but that proved inconsistent. All juices are different in viscosity. Thicker juices take longer to prime. You must be patient with priming. A carto that is not sufficiently saturated is guaranteed to be toast as soon as you hit the fire button. And there's no going back after a carto dies.