It depends on what subject you are applying for and also which league table you're looking at. UCL is apparently ranked fourth worldwide when I went there for open day, that's what the professors there were bragging about) on the QS league tables.
I myself tend to use the complete university league tables. There's loads of league tables, as long as there's interest, there's people making them, and there could always be a sense of bias to them as each table varies between each other by quite a margin. It really is up to your own opinion at the end of the day. Depends on what you value as the most and least important factors.
Regarding what US thinks, generally Russell group universities, Oxbridge, Imperial, UCL, LSE and a few others which I'm not too sure about are considered as really good unis. It's worth noting that regardless of where you study, the most important thing is how well you do. So if you went to Oxbridge and ended up getting kicked out because you failed your exams, you could still out on your CV that you went to oxbridge. But compare that to someone who went to Warwick or even lower unis (you can see examples of this on tsr from tsr users), and got a first, the company who can hire one out of the two people will almost definitely go for the one with a better grade. Work experience is also an important factor. No matter how popular a university is, it all comes down to the person itself. Hope this helps