You didn't really give any info on what you'd use it for, so people don't really know how to answer your question.
However... keep in mind that both the Sigma 30mm and 10-20mm will only work on crop sensor camera bodies. Not sure if you're on Canon or Nikon - or either one for that matter.. but if you make a jump to full frame you won't really be able to use those lenses. I'd consider the Nikon 35mm f/1.8 or the Canon 28mm f/1.8 or something along those lines.