The Quest for Efficiency

i've been wondering for some time now, what's a more efficient way designing a wing? are raked wingtips better off over winglets or is it the other way around? are steep winglets (737/747/757/767) better than added raked dihedral like on an A330/A340?

the P-8 Posiedon is going to be entering production soon, it's going to be a 737-800 aiframe featuring raked wingtips instead of winglets. would it be a wise idea to emulate that design on a KC-767, perhaps by installing the -400 wing over the standard -200 wing? since the deisgn is going to be reworked for the new bid anyway, why not get the most performance out of it? i'd also love to see a KC-135-style access ladder installed on the future design too...