Former LEOs is a no-brainer. They generally have far more firearms training, situation training, and req'd sheepdog attitude than the general civilian population -- Key on situation training/sheepdog.
Veterans have basic if not extended firearms training (at least more than the general population as a group). They also tend to have a sheepdog attitude. What they don't have -- and will desperately need -- is situation training.
The General population is the general population: a black hole until vetted through either the police and/or military strainer. Some may be simply OUTstanding. But how do you do that extended sifting beyond a background check?