Board Thread:LOC General Discussion/@comment-68.145.172.9-20130317160834/@comment-5706972-20130318161022

Honestly you will want to do both.

High efficiency is best - so if you can afford it, get the best efficiency cards and stack your deck.

High DEF power will be important when you have more DEF than your cards can use and/or you want a stronger deck. URs (for the most part) have higher efficiency than rare cards, and higher DEF power, but cost more.

In other words: a deck full of PM rares hitting at 700 efficiency, but only having <6000 DEF power should be replaced with higher DEF power URs (with hopefully higher than 700 efficiency).