I can't tell you why Suprnova performs badly like this (I had a similar experience) but I can tell you that i have not yet found a good reliable Mona pool anywhere. One of the biggest I found was asicminer.info and it consistently under quoted my hash-rate by 20-30%.
Isn't it possible that it's because of the latency? Are any of the pools near you? Some pools have definitely been having trouble with the newfound interest though. I find it hard to believe that /all pool operators/ are trying to exploit users, especially given I was a pool operator back in the day who ran my pool at a loss (1% bonus) to get more people to mine Monacoin.
I wasn't trying to say all pool operators are bad, just that I think that since Mona has had a huge amount of recent attention, and there are a lot of newbie miners out there - I think some pools take advantage of that.
As for latency problems, I tried asicminer.info asia server (I live in Australia) and when I pinged it it was always in the 200-300ms range, so I don't think that should casue huge latency.
When I use my own P2Pool node for vertcoin, using the same mining software and the same algorithm, I get credited with hash-rates that average to very close to my locally reported hashrate, but if I use asicminer.info I get 20-30% less, and Suprnova was even worse. Apparently miningpoolhub now has Mona so I may try them.
It's a shame becasue Mona's price is bouncing back again but I still can't find a reliable pool - very frustrating.