Most efficient is hard to pin down, there's a lot of factors to consider.
-Financial (cost to the taxpayer) can be measured by GDP or dollars per citizen?
-Technology (doing more with less manpower) The US is way ahead of most
-Firepower (Killing the enemy more than they kill you) depending on the size of the conflict and how well equipped your adversary is. In strictly a ground war the Chinese and Russia would inflict a big hurt on anyone but still behind the US.
-Mobility (getting there in the least amount of time no matter where it is) No contest the US. UK and France a distant second
-Intelligence (knowing your enemy, its culture, and geography) The UK and Russia spend more time and seem better at this.
The above is if you expect your military to be involved with more than defending your own border. War, peacekeeping, humanitarian and disaster assistance will put a lot more demands on a military.
Israel may be good in its region but they have no expeditionary capability.
If it's solely on defending your own borders than any small mountainous country would have the advantage. How would you invade Switzerland with only a few avenues in? They could defend those forever and make the aggressors pay.
Canada has a long way to go if it wants to simply defend its own borders. The Navy is in deep trouble and will need 30 or more new vessels in the coming decade or face complete rust out. Our arctic claims are being challenged and building a few patrol boats will not deter Russia, the US, or even China in the least...
Just my 2 cents for what its worth, fire away