For me cotton and its not even close.....bigger clouds, less heat sink effect, better taste and you don't boil your liquids with cotton. By the time I was done with the
tank some of my favorite juices would turn 100 shades darker with ss mesh. With mesh I had to adjust the coils daily to get that perfect vape while with cotton I only need to change the cotton once a week. Also with ss mesh you have to go through a whole
tank before it starts tasting right while with cotton after a few hits the cotton taste disappears. I mentioned heat sink effect but I should elaborate....with ss mesh half your power goes to heating up the mesh itself....it isn't efficient at all. You can vape at lower wattage with cotton and make bigger clouds compared to mesh. If you looked at these forums a couple years back everyone was using mesh and gennies....now very few people use gennies anymore and fewer use mesh....most people prefer cotton. I still use my gennies but have converted them all to cotton builds. Ofcourse YMMV.