You have to think differently.

Some cards are good for one or two algorithm some for others.
RX 580 are good for Ethash + Cryptonight (ETH,Monero,ETN...)

It will really depend on what you want to mine.

You can check https://whattomine.com/ to have an overview of different card.

And think about Hash/PWR because electricity have an important cost on mining.

I have one RIG of 6 RX 580 Nitro + 8G

On cryptonight: ETN I have Hash > 5000H/s for PWR < 800W
On Ethash: ETH Hash > 180 mh/s for PWR < 1000W

So ~200W and 200W in one year cost money.