Well its not a matter of which GPU is the best that you can buy, but what can you find? Not only are most all the cards at least 60% more expensive, they are also sold out. You have 2 choices with an acceptable ROI time involved. Buy a Titan XP from Nvdida for $1200 (Sorry, Star Wars Edition sold out), or Buy a bunch of 1050 ti.
It seems to me that a large number 1050 ti will be more profitable. But now it seems to me unprofitable to buy the GPU. The price of the cryptocurrency is dropping the price of the GPU is increasing. Perhaps now we need to take a break. You risk nothing. Crypto currency will rise in price. You sell the coins and buy a cheaper GPU. If demand is reduced then the speculators will lower the prices of the GPU.