I mine on Eclipse, it has been great, although the US server has gone down twice in 2 months. No biggie, I just switch to the EU server and it's all good. My first pool was Slush, then Deepbit, now Eclipse.
ozcoin has never gone down for me. Bitminter had a few issues in the past when he was updating the server/api, but even when the webserver died the mining server was still operational.