For a long time I would have said Kayfun but now the Lemo2 has changed that. Setting aside the fact that the Kayfun v4 is a beautiful thing to look at, it is a spectacularly over-engineered and ultimately flawed design. Don't get me wrong I got a great vaping experience on mine before the problems started, and it killed me to have to go looking for an alternative. Having said that, the Lemo2 has been excellent so far. Ok so I don't get access to the deck while there's juice in the tank, but as quick as it goes through juice, I don't have to wait long. Top fill works just fine as long as you remember to close the airflow (a habbit I'm working on). Flavor and vapor are excellent.
To the point about dual coil tanks... I've got a goblin atm and the word I'd use to describe the vape is 'intense'. Flavor, throat hit... intense. I've found few things wreck a cigarette craving like a few pulls on the 0.4ohm Goblin filled with some 18mg juice, but it's a bit more intense than I really like given how much I tend to chain vape. Single coil tanks are just a more mellow experience, and the choice comes down to personal preference. Anyone considering the Lemo could do a lot worse. I'm sure there are those who have KayfunV4's and have never had an issue, but imho it's solving a problem by way of creating quite a few more failure points. With the exception of the o-rings (which work fine as long as you keep an eye on them) the Lemo2 is a far simpler design that does the job extremely well.