It's always "AMD zone" or "nVidia zone" until somebody comes up with a proof that it is not... 
The ETHlargement pill worked wonders for 1080/1080Ti's. And all until then were saying nVidias are crap at ETHash.
Everyone was saying AMD is crap at Lyra2z... until Teamred showed fools otherwise.
"AMD zone" or "nVidia zone"... There have always been supporters of this or that brand. Therefore, I think that there is no point in discussing which of these brands is an outspoken leader. Everything is very subjective.The ETHlargement pill worked wonders for 1080/1080Ti's. And all until then were saying nVidias are crap at ETHash.
Everyone was saying AMD is crap at Lyra2z... until Teamred showed fools otherwise.
Because you are investing in one or the other; it is relevant.
Hashrates for a given algorithm, with a given GPU and given mining client, with a given OC: are a matter of fact.
Granted you need to look at poolside data; with stale shares removed.
Over the last years, my rigs of 570's were making a killing. Then the rig of 1080's was making more. Then the Vegas took over and smashed it with CN.
Today, the 570's are dead, i.e. I could run them but they'd barely break even. The Vegas and the 1080's are trading blows but at a much lower level.
No idea what tomorrow will bring. Hence, you diversify.