I've tried most of the newsreaders, and I keep coming back to this. It may not be as good for files as some of those that seem designed just to grab files from the usenet, but for following threads and actually participating in discussions NewsWatcher hasn't been beat yet. It follows all the standards that Outlook/Entourage breaks, and has a very full-featured filtering capability that is not hard to configure. No matter how you like your newsgroups you can probably configure NewsWatcher so you'll like it.

Only quabble some may have is the lack of an all-in-one view, but I prefer the multiple window approach.