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.
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.
They are a matter of fact indeed but the facts change over time. Crypto is flexible and evolving. Devs come and go. Prices go up and down, and what was good yesterday might not be tomorrow.
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.
I have been mining with GPUs; since Bitcoin was able to mined with GPUs.
I used only AMD rigs for a long time, the first Nvidia GPU I used for mining was a 750ti.
I only buy GPUs that are likely to be effective, efficient, and likely to have a good resale value.
1070s have been around longer than 570s, they were released around the same time as 470s.
I bought 1070's at different times; some before 500 series, some after, for prices ranging from $330 to $385.
1070s are still worth $230.
I have a hard time seeing how 570s made more sense; especially in light of the current value of 1070s.
Perhaps if you planned on only mining ETH, and spent the time to flash your GPUs; it might have made sense at the time: to have slightly lower upfront costs.
Diversification in held coins makes sense. Buying GPUs that aren't effective, efficient, and likely to have a good resale value is not a good idea.