I have all 3 tanks (5 subtank minis, 1 Atlantis, and 5 Delta IIs). In my opinion, the subtanks and Atlantis are easier to fill and clean....but for flavor and vapor, I prefer the Delta II. Although all 3 types work well, provide good flavor, and have decent quality, I believe the quality of the Delta II is a bit better.
On the downside, the Atlantis does not currently have the option of an RBA section, and the Delta II, for some people, can be tricky to fill and also tricky to see your juice level when it is assembled.