So I have been running a gtx 1070 and a rx 480 for a few days now.

The 1070 mines about 0.0005-0.0007 btc more per day than the rx 480 while consuming 30-40 watts less power. It also was about 110$ more expensive to purchase.

I have found that the 1070 is best for mining Digibyte (Skein, Myr-Gr), and Feathercoin (Neoscrypt). That is the main problem with the NVIDIA cards. They are best for mining small coins that aren't very stable and used mainly for trading.

However, there are also plans for Eth to move to PoS from PoW, which will break AMD mining. Nobody has any ideas when this might happen though.

I think it is good to diversify, since mining on both AMD and NVIDIA even on the same system is not much of a problem.