Definitely ETC + Sia better than Zec currently 
Not if you are paying power eth + SIA is power hungery by like 30% , Eth alone uses a bit more power than ZEC alone so its a no brainer to mine ZEC if you have power over .10
Personally, I still mine ZEC over ETH and my power is at $0.06/kwh. The temperatures difference means the fans run slower and therefore significantly quieter.