I personally have had really bad luck with private, members only tracker sites. If I don't get on the torrent within minutes of posting, I can't reach the desired 100% seeding goal. On the other hand, this is ridiculously easy to do with public tracker sites (such as TPB).
There is huge variability in private trackers, some are awful (Demono's adds have become unbearable), some are pretty good, like karagarga, which has lots of films I simply could not find anywhere else, legally or otherwise, and others are awesome, like what.cd.
This is the case with the best and most serious private trackers. If you're serious about keeping a good ratio, just get a seedbox and set up a script to download the torrents you want as soon as they're posted (most trackers have an IRC bot that announces new torrents).
