yeah I'll be going for gaming mostly, and for the brand I've read the page , I'm wondering why it's not included in sapphire and gigabyte models , especially the sapphire is mentioned as to be one of the perfectly balanced ones in terms of cooling, performane,etc...What scenario is the system going to be used in? If we assume it's gaming, then:
https://www.techspot.com/review/1885-ryzen-5-3600-vs-core-i5-9400f/
That review has the R5 2600 in it, along with the i5 9400F - the latter is better for gaming.
This review has the RX 570 and the RX 580 in it - the latter can be notably faster in certain games than the RX 570.
https://www.techspot.com/review/1780-geforce-1060-vs-radeon-580-vs-radeon-570/
This would suggest that the best combination would the i5 9400F + RX 580. As for which brand is the best, have a read of this:
https://www.wepc.com/reviews/best-rx-580/