Most efficient wing...

[south coast]

I have been having a debate with a friend about the most efficient wing...and by that I mean the best lidt to drag ratio.

I was under the impression, the most effective and efficient wing is a clean wing.

The lift created by a clean wing also generates x amount of drag.
Now, when trainling edge flaps are deployed, I understand that lift is increased, and that drag is also increased.

Question: Is the increase in lift and drag giving the wing with flaps down a better lift to drag ratio, better efficieny , than that of a clean wing.

P of F buffs needed on this one....

Thanks