When I think of the UK, I think "small but packs a strong punch." It's funny, though, after WW I and WW II, the British military really took a huge, huge beating. WW I was probably its height, where it was arguably the best in the world, but after that it was kinda fat and coasting, in my opinion. Then came the two World Wars in which obviously Britain was decimated. But since then, since Britain has had to rebuild, and most importantly to scale down its armed forces after losing its "colonies," etc., I think they've actually made themselves into a lot more of a smaller, deadlier military.
I sort of wonder if the USA is getting too big for its britches, ya know? Sort of like how Britain was right before WWI? Anyhow, but yeah, I agree, right now the US is still number one as far as its military might is concerned.
Speaking of which, if the US and the UK ever got into a war with each other, though, I think that the US would eventually win, but not without having our noses considerably bruised.
Another thing I just thought about is that, even though the stereotype is that autocratic governments tend to have the best militaries in the world (e.g., Hannibal, Alexander the Great, Napoleon, Nazi Germany, the Soviets, etc.), most of them eventually lost to more I guess you could say "democratic" forces. What I mean is that I think militaries are in a way more effective overall when people volunteer for them -- "citizen-soldiers" as someone like Stephen Ambrose might've said, rather than (as has historically been the case) when armies were built from mercenaries and/or conscripted against their will. So that, generally speaking, I think a democracy's military is more a force to be reckoned with than even an autocratic regime's. Primarily because in a democracy the entire people are (more or less) in support of and contribute directly to the success or failure of its military, whereas in the former the military is largely in the hands of a small group of powerful elites or even a single person.