I have used AT&T's (now Comcast) and Charter Communications' free NNTP servers for a while and they were both excellent and reliable, with retention and decent speed. Although, Charter only allows 2 connections per IP and now only allows 20 days or so of retention since they switched News Service Providers last year. I am still on Charter's free service but I can't use my connection to its fullest capacity I also use a payserver whose retention can be upto 60 days for certain popular groups, I have an unlimited download account for which I pay monthly and over 16 connections per IP costing me only $15.00.
Unless you already have a good ISP with a reputable NNTP you can possible get away with not paying for premium, I was lucky for a while but its usually frustating when you can't fully take advantage of the system/setup.