Pretty sure the only ones mining ZEC right now are the Tahiti and Pitcairn GPUs. Since if you got Tonga/Hawaii/Polaris you are most likely back to ETH/ETC mining.
I'm switching my Tongas back to eth, but my Hawaii is staying on ZEC. I get ~330sols with optiminer and ~28Mh/s with sgminer-gm.
My Tahiti and Pitcairn GPUs have been on exp for the last few weeks, since that gives me better returns than ZEC.
The other thing I don't like about ZEC is that the difficulty fluctuates +-15% day-to day, while eth (and even exp) is more steady.