I have been using NewsGator for about a year. It syncs with NetNewsWire and it has an excellent iPhone application. About a month ago I started using Google Reader to figure it out if I was missing out on anything. After a month, I'm sticking with Google Reader.
There are a few reasons for this decision. As nice as NetNewsWire is, I wasn't really using its additional features. Having a native news reading application really wasn't making that much of a difference for me. Furthermore, the NewsGator iPhone interface doesn't allow you to go back and read "clipped" articles unless you leave them "unread" which then makes you reader list cluttery.
Google Reader solves these problems and works well with the way I do things. I usually find myself going through and tagging articles on my iPhone and actually reading interesting ones on my Mac. What is your favorite reader?