For a good DL at 40W with good flavor and cloud take a look at the Baby/Big Baby Beast from Smok. Pair it with the Q2 0.4 ohm coil (the one installed in a BB, the BBB comes with lower ohm coils that you might like, but would need a higher wattage, I did have the one in the BBB works well at 50-55W) and you have nice performance, reasonable battery life, and won't suck down juice faster than you can refill it like some of the "octadeca" coils they offer for pure cloud. The vape is not a restricted air, it's lots of air, which is not uncommon for a DL cloud tank.
Another good possibility is the Tobeco Super tank. Cheap, takes any Atlantis style coil, of which there are dozens on the market, and can do everything from a mtl (Triton full size, 1.8 ohm is good for that), to restricted to wide open, pretty much based on whatever coil you want to use.