AMD video cards are the cards of choice for cryptocurrency mining.
But if you've been trying to pick up an AMD RX 470/480 or RX 570/580 in the last few weeks, you'll know that there isn't one to be had on the planet, unless you're lucky enough to find a used one.
My gaming PC has an nVidia GTX970 card and after installing some Ethereum mining software, I found the card was mining at a whopping 3 Mh/s. For comparison, an AMD RX 470 mines at about 20 Mh/s.
One of nVidia's current popular cards is the GTX 1070. These are still available, though they are more expensive than an equivalent AMD RX 580.
So how does a GTX 1070 compare in the mining stakes against an RX 580?
Recently that very question was asked where mining for Bitcoin and Ethereum is concerned.
Based on this experiment, it was found that there wasn't much difference between the two while mining for Ethereum, but while building a data center environment for Bitcoin, where the cost of electricity becomes more important, the older Nvidia chip performed better than the AMD processor over the course of a year.
Both cards mine at 20-23 Mh/s. Tweaking PC and BIOS settings and tuning the cards should get a couple of more Mh/s out of them.
So if the price of electricity is a concern where you live, the nVidia card will be a better option for mining.