Long time Newsbin Pro user here. I have to second Unison. When I got my first mac I tried every newsreader I could find and while some were decent at best, most were pure crap, especially compared to newsbin.
Then I tried Unison and after a while I really began to like it. Few of the features I like best are tabs, one tab for binary files and a tab for the text posts so I could look at one or the other easily. I don't like the way Newsbin handled text posts since it's primarily a binary downloader. Another thing about it I like is it groups files togeather. In Newsbin when you're looking for a group of files they may be scattered around based on when they were uploaded. Yes you can sort and group easily in Newsbin but I find it handy that it's done for me in Unison.
Unison took a week or two to grow on me but I really like it now and hands down better than anything else for OSX.