I'm beginning to think it's all in the preparation, guv.
What I mean is there's all that teasing out of the cotton, pulling it apart slightly to separate the fibres and then rolling it, like the Scottish roll, combing it, tickling your wicks, what have you...
...or there are cottons that have various forms of this process done for you already, so you just pull off a chunk, twist the end into a point, and slide it through your coil.
I mean, there are cottons that absorb immediately you put juice on them, and cottons that seem to almost repel the juice until you finally manage to get them to saturate (Kendo gold?).
I can wick a tank with CBV2 and do what feels exactly the same with CB Prime, and the Prime seems to just suck up more juice, to the extent that it drips down the airflow, whereas the V2 doesn't.
So I use different cotton's for DTL (CBV2 and CB Prime) and MTL (Cotton Candy Collection and Coilmaster Pro).
Having said that, so far I have found Cotton Candy Collection to be the best "all rounder".