really , any of the choices seems fine ...
if you plan on replacing it sooner , then go with Rx 570 @ 15k .. you save 4k now , that 4k will be invested better in the next GPU..
con- you will have to replace it sooner , but you will get more bang for your buck .. more performance/price
if you want your card to last a bit longer than that then get Rx 580 4gb @ 19k.. you pay 26 % more for 10% or so more performance... but it becomes crucial if you want to hit maximum fps ... and stay at 60 fps for titles like witcher 3 .. but with Freesync in place , it will not matter much if you see few drops and don't touch 60 in a few games...
8gb version to me seems not that worth it , unless you want all those high texture mods and game above 1080p ... by the time 4gb will become a real problem for most games , you'll want to replace the card anyway.. there may be a few games that may run into 4gb ram limit at highest settings , but by and large 4gb should be fine for most games at 1080p
this option seems fine if you aren't going to replace the card for a long time and want to stick with it for maximum duration , in that case you can choose 8gb
Personally i would go with Sapphire Pulse Rx 570 @ 15k and replace it sooner to get more performance/price..
Gigabyte gaming 3 should be ok with slight overclocks , if you want better audio and dual bios
but don't expect too much out of it...
you can ask RCuber , he is using one..
50K PC Upgrade for Gaming/Streaming - CPU+ RAM + MOBO