I've used both and ended up sticking with BitTorrent, because it seems that all the unlimited bandwidth & no monthly limited downloads, on Usenet, were pay-only services... Is this true? I have an NNTP server but can only get 8 GB a month, and that's just not worth the time. With BT, I get a consistent 5-10GB a day. With no limits, except the amount being shared.
Usenet did have some great rapidshare.de-like speed and consistency, but again the limits sucked.
Another thing about Usenet and sites like Rapidshare and Megaupload. Is although for small individual RAR files they're great. I find that I can quickly waste a lot of time decompressing, finding passwords, and deleting the originals, etc... With BT, I get 90% files in non-RAR format so it saves a bunch of time too...
I wanted to use Usenet because everyone says you can find so much more in it, but I will be honest I didn't find much, though I only gave it a few days, because I hit my 8 GB limit that month....