Like bassnation I'm in west dulwich and it rocks IMO. There's lots of green space round here, the parks are really good, you can get pretty big flats for not much money relative to Brixton/Clapham, transports OK, etc.
Brixton has changed a lot in the 10 years I've been in London, it's pretty safe and middle class now. There are bits of the old Brixton if you look for them, like the University Of Dub nights and the Hobgoblin pub, but a lot of it is upwardly mobile, aspirational, etc. It's not as bad as Clapham yet, but it's going the same way. There's only a couple of old irish pubs left in Brixton now.
Forest Hill is a really, really underrated place. There are some amazing houses in Forest Hill, and the wholefood cafe opposite the old swimming pool is the best cafe I've found yet in London. The Horniman museum is wicked too. It's kind of cut off from the Brixton/Clapham nexus for public transport, so most people who live there have social circles going over to the east (Lewisham, Catford, Greenwich). But if you're at Goldsmiths you might find that anyway.
The most unsafe places in South London are further out, like South Norwood, Mitcham and Croydon. I've lived around Brixton/Herne Hill/Dulwich for over 5 years and worked in a couple of pubs, and I've rarely seen bad trouble. You'd be very, very unlucky to get caught up in something unless you went looking for it.
you do have to watch yourself, as there are alot of predators about.
That's true, though. The standard caveats of urban living always apply.