Which country has the best, most efficiently trained soldiers in the world?
The USA is obviously number one, but after that, Israel, the UK, and South Korea come to mind.
If your criteria for "best" is efficently trained, prepared, etc. then I would agree with the United States being number 1.
We have technology, mobility, flexibility, and options with respect to the mission each branch operates in. I feel that we also hold back most of the time in order to prevent collateral damage and the negative blowback from that. If we simply made it clear that we, as a country, could care less about collateral damage, and made it policy then I'd say that few would @#!* with us at all. Our morality and the outrage of our citizenry prevents us from say bombing a city block flat with a daisy-cutter should there be one single innocent non-combatant present.
The UK is also solid for historically good training, high success rate. Diversity of forces, esprit de corps.
China - for mere mass. Massive numerical advantage can trump a lot. Good technology, I suspect that rigorous adherence to the party line kills some initiative. But China is still scary and the current century is being predicted to be a Chinese Hegemony much in the same way that 19th cent was Britain, and the 20th was the US.
India/Pakistan - Mostly because these two have been at each other's throats for so long that they have had good practice killing each other, and can learn from their mistakes. Too bad they can't stick to cricket. The world would be a lot more secure.
Russia - Technology, mass. The Balkanization of the old Soviet knocks them down a touch, but the old Soviet Union/Warsaw Pact was the monster under our beds for the longest time.
As far as the rest? It's hard to say how efficiently they are trained. Especially if you take the country as a whole. Conventional forces are all basically the same. But each country has some real hard special forces that could match up with the rest pretty well. Particularly those that are trained for one specific mission. It would be interesting to read a discussion of various Special Forces around the world.