Obviously it is relevant to the degree course/university you are applying for (as some people have mentioned). Of course it also depends on how snooty the admissions tutor who looks at your UCAS form will be. But remember, this thread is about the "most respected" A-levels and not the "hardest".
From my own intuition, other people's opinions (teachers, admissions tutors, lecturers, uni deans etc), I would list the subjects in three tiers of respectability, thus (and not in order within the tier):
TOP TIER (Tres well respected):
English literature
History
Physics
Chemistry
Biology
Geography
Art
Music
Economics
French, German, Spanish, Latin (all the languages)
Maths
(These top tier subjects tend to be core academic subjects which are intellectually challenging, but crucially, have been going a long time. Fail safe.).
MIDDLE TIER (respected by most):
Sociology
Psychology
RE
Business Studies
ICT
Law
English language
etc
LOWER TIER (hmmm):
Media Studies
PE
Travel & Tourism
Photography
Computing
General Studies
Critical Thinking (I think it's more of a low than a medium but it is borderline)
etc
Obviously this is all relevant. If you are studying Physiotherapy or something at uni, PE might well be an asset. If you are applying for law, it most likely will not be.