Hello Bryan,
Thank you for your question, based on our CNC machines if you are planning on milling soft woods and plastics I would recommend the standard Nema 23 Motors.
If you are planning on milling Hard woods and soft metals like Aluminium I would recommend the Nema 23 High Torque motors.
Otherwise if you are building your own Custom CNC machine we would need to know how heavy your axes are and what materials you are milling.
Hope this is helpful.
Kind Regards
Aaron