Mach 2/3 Arcs, is what you would use for normal cutting jobs.
Mach 2/3 ATC Arcs, is for when your machine utilizes an Automatic Tool Changer. (ATC)
Mach 2/3 wrapx2a, is for rotary work where you are wrapping the X axis around your A axis.
This is dependant on how your rotary axis is set up. You may need to use Mach 2/3 wrapy2a instead.