started with cotton, them jumped on the degummed hemp fiber wagon, now using Ramie Fiber for all my wicking needs. IMO, both hemp and ramie are far superior to cotton. Wicks better, lasts longer, more heat tolerant. All fibers have their own unique characteristics, so there is a learning curve on densities and amount for each application.
For cotton, sterile and organic seem to be best. Are you wicking properly, have the correct densities
through the coil? Some of the tastes you are experience could be shades of dry hits and or hot spots in the coil. When used cotton, would boil mine 30 minutes, otherwise got a cottony taste, and wick does take a few ml use before broke in and fibers fully saturated.