I can't claim to understand exactly what efficiency means in the military context, but it seems fairly obvious to me that the best military force would be the one that's recently fought and won most often. The Swiss Army may be superbly equipped and run brilliantly, but when was the last time it fought anyone? Combat is the only meaningful test. The best would have to be the IDF, the Israeli Defense Force. In the last 60-something years it has fought every one of its neighbours singly and together and thumped them all convincingly, sometimes against apparently overwhelming odds. No other military force on the planet has a record like that.
