It depends on WHAT you are mining.

 1070 ti is the most efficient card at ZEC mining right now with the 1080 a close second (but worse on hash/$ at any setting and the 1070 and 1080 ti are both fairly close on best efficiency OR hash/$).

 For ETH the 1070 matches the 1070 ti hashrate exactly (same memory system on a VERY memory-hard algorithm) and the 1070 blows the 1080 completely out of the water - the 1080 ti beats the 1070 but not by a lot, making the 1070 by far the hash/$ leader of those 4 cards on ETH.
 SOME 1070 cards will mine ETH at 32 Mhash/s but many of them do good to get to 30 - but even at stock clocks they pretty much all do more than 28.
 But for $400 OR MORE they are not cost effective vs a 1060 3GB card that does 22+ for about half the cost, and they are not even CLOSE to cost effective vs RX 470/480/570/580 cards in the UNDER $250 range that can generally get to 28-30 Mhash (with BIOS mods) and are very close on efficiency.

 Then there is Monero, where the Vega 56 is the current king of hash/watt (though some of the NVidia cards can argue there) and *WHEN* you can get one at semi-close to MSRP the hash/$ winner by a LOT.
 Vega 56 is even beating those old "open-compute" refurb Intel servers on hash/$....

 If you can find a Vega 56 for under $500, it currently has an ROI in the 85 day ballpark, and has been consistantly under 105 days for the last couple weeks.