Hi I am still new in mining, but as far as I know, your GPU also plays a factor on what to mine. If I am not mistaken, some cards were good at dual mining ETH and Monero while others in ETH and ZCash. Also, it is best to if ETH hashrates were not affected by dual mining other coins. I've read somewhere that dual mining ETH and Sia does not affect ETH hashrates at all.
For your information kapipindot,
If you want to know what is the best coin to mine with your specific GPU, go to whattomine.com and enter the number of cards you are mining with on the top section and then press calculate...
With claymore v9.8 or higher dual mining does not affect your ethereum hashrate anymore. So you don't have to mine SIA which is quite low right now so I am pretty it is not the best to dualmine.