From my experience with clones, my Hcigar Stingray is the hardest hitting with very little voltage drop, in the 0.08 range vs. my EHPro 69 which has a 0.3+ voltage drop. Both are fairly inexpensive, though I think I did pay around $10 more for the Stingray clone. The Stingray however has a stickier switch despite being magnetic, so take that into consideration.
As for tanks, right now the best Kayfun clone seems to be the Tobeco Kayfun Lite Plus Black Edition. I have both the BE and a standard Tobeco Kayfun clone, and I can tell you that the Black Edition is superior, not that it's saying much. Both vape pretty well, just the BE has fewer quirks. I've also got an Hcigar Kayfun 3.1 clone which actually vapes better than the Tobeco clones, but I all but destroyed the fill valve using a metal blunt tip needle to fill it, so that's a HUGE negative unless you are aware of the problem before hand.
If you can avoid the Kayfun hype, then try a Winsmoke SQuape clone. Hits like a champ, super easy to build once you get the hang of it, and you can work on the coil without having to empty the tank. It's a very heavy atomizer though, and a little more finicky than a Kayfun clone, but once you get it figured out, it is a much better atomizer. Just don't be afraid of building the coil REALLY close to the deck. The higher the coil is above the deck, the more it's going to flood and leak. Build it closer, and it's going to treat you right.
