Whichever is cheapest. There's even a good chance that one or two of the 0.40 pack will read 0.45-ish and one or two of the 0.6 pack will read 0.55-ish.
I challenge anyone to vape'em at 50 Watts and tell the difference.
Accepted. Could be the juice. I am using the .04 coils on my Smok, and vaping at 55 watts on the baby beast, personally I found the taste just really pops harder, and its allot warmer. In short, it really matches the cig.
They swear the .06 will really eat the juice, and imho, I just found that to be true. Just keep in mind, wattage, flavor, what tastes better is all subjective, that just works for me. You may find it is different for you.
I am getting ready to try something with the coils I have seen allot about. Once a week, take out the old coil, clean it, set it aside, then pop in a new one. Then week later, clean the coil set it aside, and try the one I cleaned a week before. Rinse and repeat. Be fun to see how it works out.