Undoubtedly the classics help with learning about different techniques and approaches. Not every classic is like Austen though - that's why it really pays off to read widely. I read as widely as I can, choosing books that are completely unrelated to each other. If I've read some fantasy, then I'll go for something non-fiction next, or perhaps a thriller, or whatever. And I find that this helps to stop me from copying any one particular style as well - if I'm writing fantasy, and I only read fantasy I start to find that the work I'm producing is really not original at all, and my work starts to really resemble that of other authors.
Reading anything at all is essential to learning how to write. I've learned so much in the past two years from changing my reading material. Genres that I'd never been interested in before, such as crime or romance, have opened up whole new ways of thinking to me. Invaluable.
To answer your question more directly, I don't think there are particular genres that help more than others - all kinds of reading has something offer, even if it's just to teach us what NOT to do!