12 V input to multiple 5 V outputs?
Option 1 is the simplest and probably least expensive, since you only have a single supply plus 4 MOSFETS.  

Option 2 could be done without MOSFETs by using a regulators that have an enable input.  

Note that because of the large voltage differential and high current, a switching supply is the best choice.  That means that option 2 has 4 inductors, which could be a significant difference in size and cost.

A third option would be to use a single high current switching supply to convert 12V to ~5.5V, and then use low cost linear LDOs with enable inputs to convert the 5.5V to 5V.  This has the added benefit of reducing the switching noise in the 5V output, since the final stage is a linear regulator.