I like Boge cartos, have tried several different ones. I routinely get 10-14 days from each one, mostly at about 5.x volts. I use 3 ohm ones, so this is about 8.7 watts. Keep them wet, they will always last longer. Carto tanks should do this.
Admittedly, by the last couple of days the flavor is down, but vapor production is still good. I use mostly clear DIY juices, usually 80/20.