Depends on what your "starting position" is:
Replacing the Shimano cranks on your current bike to get power? ==> Magene PES P505 Base is one of the easiest and cheapest ways to go!
Building a new bike?
Going for "good enough" ==> Magene PES P505 Base
or weight weenie build? ==> Standalone Magene P505 spider + lightweight carbon cranks or Easton based PM + cranks