Safari seems to work absolutely fine on iOS 8. There are plenty of things that aren't just fine, but the browser isn't one of them. It finally uses per-tab processes which should significantly improve stability.
As far as I know, no browsers yet support WKWebView (the new Web view supporting Nitro as well as a ton of other improvements.) If there is one, it must be pretty obscure. None of the more popular alternative browsers support it yet.