All basically good suggestions above, I've been on most of them and have been on Giganews for 3+ years now; so any of my comments on the 'others' are hazy rememberings and with the leaps and bounds improvements by just about everyone during that time, maybe it's time to 'think' about switching.
BUT... it all comes down to how much your time is worth, chasing down bad or corrupted parts, downloading that last PAR file, machine/CPU time recovering things, needing a 'fills' account somewhere to backup your primary, ect. Giganews was and remains the most $$$, I moved to them from having Usenetserver (plus a fills account), because I simply got tired of tracking down huge chucks of missing crud. But, like I said, that was 3+ years ago. RIght now, I'm probably too lazy to change.
But again, in some 600GB in the last couple of months, I had 1 (ONE) block corrupted from Giga. That's how good the s/w is these days, if the originating server sent it out, come **** or high water it will be complete at any of the major servers. And most of them seem to be increasing retention by leaps and bounds in direct proportion to the cost of HD space (which means they should be passing 200 days by the end of this year... if not 300!!!).