You've got some catching up to do buddy, PD are out of business. But fear not there are plenty of viable alternatives. Before you get deluged with recommendations for models that you haven't heard about, I'd suggest looking back through the front couple of pages of the Vaporizer discussion section. The market has come a long way in a short time.
I think that we should have another motto of "there is no most efficient vaporizer". It's really imprecise terminology that's pretty meaningless
. Again it's discussed at length in a couple of specific threads, but it's the vaporist that makes the vaporizer efficient in the subjective context I suspect you mean. I think you mean a vape that will help you to slow down your consumption? In which case, yes, logs are good to look at (UD, CRZ, TT, HI, WDZ, PD), and the launch box perhaps. Anything with a small bowl to load will help you to this ends.
Also bear in mind that log vapes are generally fixed temps. How does this fit with your notion of efficiency? It's arguably inefficient if it's leaving goodness behind that could easily be extracted at a slightly higher temp, but some people don't want that so for them there's no loss of efficiency.