If you haven't checked out the Vapefly Galaxies MTL RDTA yet, you really should. It produces more vapor and flavor than anything else I know of. It uses a single coil build and your coil tool sits across the top while you are installing your coil. So you can't place the coil in the wrong spot.
The airflow hits the coil from the bottom and from 2 sides. And all 3 points are adjustable. OMG it is so perfect. The deck is like a RDA and a 2ml (yeah tiny tank) sits underneath genesis style. I think of it as a RDA with a 2ml drip well, as it does the same thing. Except it has a wall between the 2 and it doesn't leak. And filling the tank is super easy.
This has been a huge game changer for me. It even comes with a squonk pin if you want to go this route and super easy to squonk with to boot. And the only way I ever got it to leak is to overfill it or hold it upside down for a few minutes. Yes it can be held upside down for awhile before enough seeps through the breather hole between the tank and the deck. And you can get juice coming out of most tanks out of the AFC from condensation. Not this one, it stays completely dry.
Vapefly has other tank Galaxies too, which I don't know much about. But those the design are more typical of your average RTA, along with their common problems.
Vapefly Galaxies MTL Squonk RDTA – VapeFly.net