hard to tell... id say the only way to tell would be in war but you know...Usa army is the most famous one but that doesnt make them the best... chinese, russians, brittish, even Colombian. Iraqi, japanesse. all of them pretty much domain their territory very well, and since the United Nations organization was formed i highly doubt they will use their full potential ever again. (hopefully) Ask your self which armies are the worse thats way more interesting :). But if you want a direct answer for your question. Id say the brittish, russian, chinnese and iraqi armies are quite formidable. Mainly because their actions are kept in secrecy unlike the US army. USA it is also stunning. (many people say it is the best) but many people say that their actions are quite predictable.you know... 9/11 "wew aaare going to iraq" obama "we are going out of Iraq"