I would vote ipv. but personally, I never feel the need to go above 12ish watts.
Kayfun 3.1 is the best tank ever. Have to buy coils gets pita qwick. But my kayfun v4 is in the mail, so my opinion may change.
its takes about an hour to figure out how to build a kayfun.
sure its longer than the 1 minute needed to learn the kanger/aspire, but totally worth it.