I personally think that there are 2 general viewpoints to look at the question, the first is to take the "power" in absolute context, eg. the greater the quantity, the more powerful, second, is to look at the quantity against the population or land mass ratio.
In terms of the first viewpoint (gross/absolute power), Russia will have to be the most powerful in terms of their nuclear capabilities and conventional force. Ok, it is hard to say Russia being entirely an Aisan country (as part of Russia is in Europe), then China would be the most powerful given their nuclear capabilities. I doubt China will win a conventional war against Japan or India but when they have that many nuclear bombs at your disposal, I guess we have to admit that is just absolute power.
In terms of power per capital, Israel would definitely be the best. Israel has many times proven that they could defeat enemies with a strength 10 times their own force in all aspect, from land warfare to air warfare. Only their naval forces has not seen too many actions except a couple of exchanges between themselves and the then mighty Eygptian navy. Israel lost a destroyer while the Eygptian lost a few smaller boats.
In terms of the "best armed" armed forces in conventional weapons, Japan would be the best. They currently posses the best air force (most advanced American jets), the most advanced naval ships with Ageis and standard missiles, and one of the most advanced tank, the Type-90 based on German Leopard 2 tank design. Israel will be the equal first. South Korean would be second, and Thailand probably third.
In terms of numerical superiority, China, Vietnam and India could possibly fight for the #1 spot.
So, there is no real answer to this question.
If the answer is, who would probably win a all out conventional war, if everyone is fighting everyone in a marlee, then, I think Australia will win...
