I agree it varies, but what I've read (not mainly from the media, but from government and academic reports) still doesn't paint a particularly pretty picture overall. For example, here is the Bureau of Justice Statistics on prison rape: http://www.bjs.gov/index.cfm?ty=pbdetail&iid=1149

And here is the Government Accountability Office on overcrowding in the federal prison system: http://www.gao.gov/products/GAO-12-743