From my (somewhat limited) understanding of GR I know that there are two different kinds of solutions that produce a black hole, some that rotate and some that do not. What I can't figure out from my reading so far is which of the two is considered "typical" (if either). That is, when we think we have detected a black hole in space, do we initially suspect that it's rotating or stationary?
My naive assumption would be, since they form from collapsing rotating stars, that most black holes would continue rotating after formation, increasing in speed as they decreased in volume. However, I see a lot of discussion about black holes that use Schwarzschild's equations, which describes a non-rotating object. Is this merely because those are easier to deal with and "close enough", or is it really believed that many black holes are non-rotating?