You hardware config is good enough for two 570's. I like to mine and hold my coins for 4-8 months. So I look for coins with potential for high future growth. ETH rewards have been quite stable (although not as good as they used to be a few months back). So if you would like to cash out every now and then, I would say go for ETH. You can find out the most profitable coin at this website.

https://whattomine.com/

Plug in your numbers; i.e., number of 570s, electricity unit cost etc. This website will tell you how much you can earn and which coin is the most profitable.