Depends what kind of
coils you plan on building. Standard, like what you find in a Protank Head? Micro coil, like... well micro coil? Hmm what else is there aside from sub ohm? I honestly don't know. But those are your usual suspects anyway.
Cotton is hands down the easiest wicking material to use. It's easy to manipulate. It's easy to install. It's just as easily replaced. It wicks
very well, and the flavor is outstanding. It takes a little time to get used to it and learn the nuances such as knowing when your next hit will be a dry one.
Is it the best? I haven't the slightest. Plenty of other options. Silica. Bamboo. Hemp. XC-116. SS mesh. Wool. Rigid ceramic. Steel cable. Jute fiber. Probably more. As I type this post I'm waiting on some 2mm organic hemp I just got in the mail to dry after a good boil (or
three).
Cotton is still a great wick and pretty much all I use.