The poll needs another option.
"Variable"
With smoking regular cigarettes, a smoker would usually settle on 1 particular brand, and smoke at a particular rate.
Once the smoker lights a cigarette, the smoker has an incentive to smoke it, even if the first half was enough.
With ecigs, there is a whole lot of flexibility.
Many people end up having a few tanks or cartriges ready for a puff; You can pick up one thing and take a puff, then put it away, and later go puff something else if you want to.
In my case I vape mainly a low to 0 nic liquid, but I keep a v-nano with I think its 22mg/ml 'cuban cigar' which I might take an occassional puff on. I don't even carry that v-nano on me or carry it with me; it is just right here next to my computer and that's where it stays.