I, like many Microsoft MVPs, spend a lot of time poking around newsgroups and various news servers. My weapon of choice for this activity has always in the past been Outlook Express. Every once in while (because of various bugs and annoyances in OE), I look at some other news client. I have tried Gravity, had a brief look at Agent. Somehow they just didn't seem comfortable.
Currently I am trying Dialog. It is extensive, with tons of features, but it just doesn't feel right. I will use if for a couple of more weeks to see if it gets any better (maybe it is just too feature rich) -- and if not I may find myself back using Outlook Express.