"Best" is so subjective. It depends on the device with which you're driving it,. It depends on the material with which you wick the coil. It depends on the juice you're vaporizing.
What's "best" is what works for you. I don't sub-ohm with my kayfuns. I don't want to risk melting down the insulator between the deck and the block. What's "best" for *ME* is about 1.8-2.0 ohm coil, wicked with cotton or rayon, firing around 11W without any dry hits.
The beauty of the kayfun or any other RBA is that you do exactly that - rebuild it if you don't like the results you're getting.