this is a really difficult question to answer but i'll try and give it a go! it varies with universities. oxford won't actually care (in my opinion): becuase they interview their candidates, really your subjects are the least important thing in your application (your personal statement, written work and interview will be much more important) and so i don't think oxford would mind - in fact, it might make you stand out!
however, being totally honest, lse and ucl are so annoying when it comes to applications. they just have so many applicants, and they don't interview, which means that they have to find everything they can to differentiate candidates. let's say the lse application team have two completely identical applications in terms of ability, apart from one does history politics and maths, whereas the other does history politics and art. they're more likely to pick the first, because it shows more intelligence. whereas oxford doesn't care because the interview tells them almost everything they need to know about you anyway.
i can't tell you which one to pick. i'm not an admissions officer so i don't know how much what i've just said is even true! sorry, i've sort of just word vomited onto a page here with my opinions and haven't really helped lol.