Unison is currently your only really good option for binary-centric Usenet downloading. It's got some really spiffy features, and is very easy to use.
That said, if you want raw, unadulterated power, then you must have Thoth. Only one problem... it was discontinued a while ago, although many (like me) who paid for it are still happily using the last version.
The good news is, the author is looking to resurrect it, but only if there's enough interest. I'd read up on Thoth, and if it looks like an app you'd be willing to pay the modest license fee for ($25 if I remember, and you get a LOT of free updates for that price if it's under active development--there was usually a new minor release every couple of weeks with tweaks or improvements), then e-mail the author and say so, so we can ALL benefit from its resuming development.
You'll be happy, I'll be happy (oh, how I want it to be resurrected), and many other people will be happy because when they come to the Mac with the exact same question I and others will be able to say "Unison for neat interface and ease, Thoth for raw power."
Here are screenshots of the potential new versions:
http://www.cortig.net/Thoth
...and the page from the author with contact info if it looks interesting:
http://home.earthlink.net/~thoth-help/