I personally have a liking for the Safari style RSS handling, but when I'm using other systems I use Google Reader, it really works well for a web based app.
If you want something that's a Cocoa app and free, you want Vienna. If you want something better than Vienna, and don't mind paying $30, you want NetNewsWire. If you like a 2-pane approach, and don't mind paying $20, you want Newsfire. If you want something web-based, you want Google Reader.
I'd start with Google Reader and if you find it lacking in OSeXy-ness, "upgrade" to Vienna. If Vienna doesn't have the polish you're looking for, give NNW and NF a try and see which you like better.
I've been using Opera for years, a perfect all-in-one browser/email client with great filtering and rss functionality/chat tool and what not, beats anything I've ever seen