Jesus, one of my worst experiences in the military was at Ft. Hood when we had to do a live fire walk and shoot. Nothing very hard or complicated. I still to this day do not know how I managed to walk off that range with the back of my head intact. Live fire is great training, but only once everyone is up to that point.
As for which ones is best, I think it depends on what type of training is being conducted. CQB type, going to go with sim rounds. But if it's anything past 15m or so about the only thing I've seen be of any use is MILES (which by the way is still a piece of shit)
I've paint balled, but for me it was more a hobby then anything. I think it would be good for building teamwork and confidence but that is about it.
Never done Airsoft, but doesn't seem like it work very well beyond what paintball could do and leave way to much open for "I shot you first!" "No you didn't I totally got you first!"
Simunitions hurt just enough to let someone know they got shot (unless you shoot your buddy in the balls...) but after 15m or so they start doing weird things, and they don't break all the time but nothing is perfect. Think the sale of em is restricted to LEO/Military
MILES is damn near worthless but has the benefit of longest range, as long as no one is hiding behind a blade of grass
and you conduct all your training on flattop with no false cover.
I think a combination of Sim and MILES would be best. I think there is enough powder in a Sim round to "fire" the MILES. So you might get some medium/long range hits in, but when you worked your way down to close range you don't have to deal with that bullshit of "safety kills" which becomes even more a grownup case of Cowboys and Indians.
Can you tell I just got back from doing some exercises?