The End, Turnmills and The Key, The Cross and The Canvas are all closed now. But when they were open I always found the crowd to pretty sweet. All generally there for the music, whether it be DNB or any other type of music. The End in particular was my favourite due to the soundsytem, location and general vibes.
For the clubs that are open Fabric is a fucking good club, nice layout and mint soundsytem. But like most clubs in London it's on the pricey side in terms of drinks. I've also seen an increase in violence at the club too which isn't healthy. I'd stay away from places like Brixton Mass, Brixton Carling Academy etc if you're looking to avoid the sold called 'dodgy' clubs. Saying that anywhere can be dodgy these days. Brick Lane, Shoreditch are wicked areas to go out in, always loads happening down there. Clubs such as 333, 93 East are pretty cool.
One more thing. Matter is the way forward. I recommend it to anyone, simply incredible in every way possible. It provides the perfect raving experience. There's loads of other smaller clubs in and around London you're guaranteed to have a good night out in too.