nobody knows ?
Biggest thing is do you want an OS that's ahead of the curve and allows you to mine what you want to mine (pimp) or do you want an OS that's restricted to only the brand cards, coins and miners the devs choose to support (ethos)?
PIMP - loaded with all the main miners to GPU and CPU mine any coin you would like and supported Nvidia GPUs before it was "popular" - $39 per license
ethOS - can only mine a hand full of coins (Monero/ZCash/ETH) and just recently started supporting Nvidia now that it's "popular" - $39 per license
I've used both and even spend time in the pimpOS IRC and Discord support channels if you want to stop by and ask more questions. As a user of pimp I get more for my $39 using pimp than I do out of ethOS but that's just me.