^^ More seriously, Dubstep is a genre that evolved from D&B, it uses many of the same signature sounds but it is fundamentally slower, around normal dance tempo (135-150bpm). It's also quite minimalist, which it has to be to accommodate large quantities of bass frequency into the mix.
I quite like both genres but have recently gone off Pendulum with their pop-structured drum and bass tunes. I liked them at first but feel it's getting a little samey now. Dubstep will go commercial soon, Katy B's Katy on a Mission is Dubstep with the pop vocals, it's a big look and I'd expect to hear more like it coming out in response. I know a few dubstep DJs looking to make a couple of records like it to cash in quick (that said, I don't think they have the weight to "make it" alone.).
I vote for Dubstep, it's just a bit fresher at the moment. Many D&B DJs are going Dubstep, which could mean we've seen the height of D&B already.