Picked up a Delta 2 tank and iStick 50w yesterday as my 30w doesn't seem to want to hold a charge. Good timing for an upgrade.
I've only tried 1 juice in the Delta 2, but so far it shits all over the Kanger Subtank mini. The vapor flavor, density, and overall quality is excellent. Filling the tank is slightly more difficult than the subtank (which is about as easy as it gets), specifically when using the standard droppers, but I think it's just a matter of getting used to it. Also of note, the Delta 2 operates around 20 - 45 watts. I'm running it at 35w, .5ohms, which seems to be a sweet spot for me. The vapor comes out at a perfect temperature, wheres I found the subtank was hot after about 22w, and the stock drip tip got quite warm as well.
I don't think I'll be messing around with RDAs again for a while. Now I just have to wait for my order of The Looper.