Help with unregulated [car] 12v dc —> 5v dc @7.2 amps

[mvs sarma]

All said, for this type of application, the best appears Switch mode psu.
even an MC34063A based design for 40 watts or so would work efficiently .
there are many such designs.
please , at least study, if not use, the Application note attached.

 

[crutschow]

The junction-temperature on each of the three regulators will be lower than that of a single regulator and there will be much less chance of three regulators failing, than the single high-powered regulator.

That's only true if the single regulator has a similar thermal resistance from junction to case. Typically, higher current regulators have lower thermal resistance from junction to case so the difference would not be that much.