There has been a long time speculation that there is something causing 20% loss of earnings in the exchange process.   I discovered that the AverageIncrement function used to create a rolling average of the prices on the exchanges could return 80% of the input values if either of the inputs were 0.  I've submitted a bug fix to the Yiimp git, but it has not been accepted yet.  Ahashpool.com has implemented the bug fix long ago and I have found that it pays out much better than Zpool.  The one drawback is that it does not have near the same number of algorithms and coins available.  Specifically the Equihash implementation in Yiimp is private and not shared publicly.

Zpool does still pay out better than what Nicehash used too, but there is an obvious bug that continues to go unfixed.  There is a thread where evidence was presented that clearly showed that the exchange rates being given on mined coins was always 15-20% below the expected value at the time of payout.  Its a hard discussion to win because everyone seems to doubt the validity and chalks up the evidence as somehow doctored or could be explained away by exchange price fluctuations.  Hopefully Crackfoo comes to his senses and implements the bug fix.  In fact I think people would be fine paying a 5-10% exchange fee if he were transparent about it.  It costs money to run a pool and I don't think anyone expects him to do it for free.