OPS is probably the one you want. RED has more selection but also a very difficult economy. OPS still has a great library and the economy is far more manageable. Of course you will still need to build up a ratio if you're planning to download a lot
You might want to get on a general tracker like TorrentLeech that has 0day scene releases. But you won't find as good retention on older releases. It works as a nice supplement to a more selective tracker.