The free (e.g. ******) are shit. Retention (maybe 2 to 3 days) and completness (80% to 90% most of the time) is poor. The ISP are doing it for free effectivily, they are not charging extra for them, they will not reduce your fee removing them. In the US the big ISP have removed their own news servers.
There is NO comparison to the paid for ones. Giganews.com has between 190 and 200 days retention with over 99% completeness for $25 per month. Newshosting.com has around 70 days retention for $175 per year. Neither has download limits, both will max out your connection (even on 50mb connection).
As for NZB sites, the one you mention that is now closed to new anonymous members has over 150,000 NZB files available. To be honest even the free ones are good.
For me personally, there is no contest between torrents and usenet. If you are happy with torrents then stick them. They are free but they have risks associated with them and download speeds are variable.
If there any posting with viruses on usenet then 99% of the time it will get reported on the NZB sites as being infected. The downloads are more anonymous and as stated above, you are guaranteed download speed (well whatever your ISP can manage).
BTW: giganews do a 3 day, 10GB trail for free, though they will take your CC details and automatically sign you up unless you cancel. If you want to try the service out. If you want to sign up then let me know and you can put me down as the recommender.
Defo worth paying. The one above is only 7.5 Euros worth a go and if no good try another there are loads of them. The torrents are dodgy, you end up downloading stuff that isn't what it says it is full of viri (Virus's?)etc etc ng's are better imho