I've lived in London for 18 years, moved here for uni and stayed. I purchased my first flat in Streatham and hated every minute of it, I never felt safe walking around the area and it never felt like home. I've recently moved further out to Surrey.
Of all the areas you've mentioned, well I'd say they are all pretty dire, most of London is these days, unless you're fortunate enough to live in Chelsea, Kensington or Knightsbridge. But saying that, all areas have their good and bad parts.
If I had to choose from your list, I'd select Tooting, but that's because I know it quite well. Tooting Broadway is very multicultural, has a very busy shopping high street, markets, an underground station, which is rare for South London and has many bus routes.
It might be best for you to select areas easy to commute to and from university and then spend weekend looking around these areas. Also your uni may be able to recommend suitable places to stay, most have their own campuses.