Imperial. I was having second thoughts for not applying there, because of its reputation, £5000 bursary and for the course I was interested in, 'Environmental Biology and Ecology', it had lower requirements than Natural Sciences which I had applied for elsewhere. However upon looking at the employment figures for that course, only ~75% were employed/further study after 6 months which is worrying since it was a decent sample size, too (~100), this figure is usually over 85-90%. I can only guess that it's because it may be a new course or they specialise quite a lot in the maths/physics/engineering side of things which they are known for, but not so much biology.
This UCL bashing is quite worrying too, I have an offer from them for natural sciences and from Durham too, my top two choices. I wonder what is wrong exactly (except for the extortionate rent which I have heard about) or are they students from a 'rival' university by any chance?
I'd say Nottingham and Manchester for being underrated. I think the only reason for their lower ranking is because they have so many students and such a wide range of courses, but they deserve more recognition.
Warwick is an interesting one... I didn't apply there but the people I know who did apply got offers from them within a few weeks, but seem to have written them off completely, for various reasons including 'it's too modern', 'ugly', 'prison-like, terrible accommodation'. Perhaps its underrated in some regard? It claims to have always been in the top 10 since records began but I don't know many who have it as a first choice.