As
tenebriscaelum said above, let's ignoring about prices.
Work well isn't the best right? It's more like still profitable for using.
at The red sides (AMD)Vega 56/64 seems the most ideal and sturdy for the most algorithm.
RX 580,570,480,470 still having flavor, 8GB is better, and 4GB still can fight.
at The green sides (Nvidia)
1080Ti and 1070Ti seem the leader of the green troops. Both can beat the leader of the red troops in a few algorithms. With significant efficiency Watt/Hashrate. And may we need to add 1070 and 1080 (not Ti) at the bottom of the leader.
In the middle class of green side, we can found 1050Ti, 1060.
Or Else, you can be more patient for a couple of month for newest series.