Well i doubt this thread will last long but oh well, im going assume you mean combined forces not just the army. So....
1. US of A - Light years ahead of anyone else in many areas, high population, good nuclear areasonal, dominant airforce, unchallenged navy. I think the number one slot is pretty well obvious. Still the only naiton to project power on a global scale in large numbers. Vast natural resources and a strong warrior history.
2. Tough but probally Russia. Huge nuke aresonal (effectiveness and readiness is arguable.) Still a huge fleet with many diffrent kinds of vesselts, however the tech is ageing and theres not enough funds for maintence. Still have powerful R&D firms without the money to produce what they desighn in significant numbers. Sizeable population, vast natural resources and huge poretial for growth make this my #2 choice.
3. China. one word numbers, huge amounts of antiquated equipment most of which doesnt work, and enough troops to bridge the pacfic by standing head to toe. (this is a fact) Starting to get some to date tech, decent nuclear aresonal. Growing economy and modernizing military and HUGE manpower mixed with nationalism make this a regional power.
4-9 EU Can be compared to well rounded pebel not excelling in any one particlar area but can do it all with some effectiveness. Decent amount of manpower, decent tech but wihout the funds to produce high tech weapons in substtional numbers. Liberal culture is rather anti-military and donesnt support military operations very often. Ablity to project power on a smaller scale than the USA, but still has a sizeable nuclear aresnal.
10. India, basically same as china but on a smaller scale.