There is a lot of talk about Thoth, but with no development for years and none planned leaves you with Unison. A lot of people seem to dislike it, but I love it. It rips through multi-million message groups without a problem on my G5. It displays messages and binaries in a way that makes sense to me and I have no usage problems with the program. The last couple updates added binary upload capability.

I've used Thoth in the past, and it was/is a fine newsreader, but it can be daunting to a first-time user. Unison to me is great for a first-time usenet reader user. Hardcore users may want to stick with Thoth, though I personally see no reason why Unison can't work for just about any type user.

If you need a Usent Reader for OS X, then this gets my recommendation.