[2020] Best mining layer?

You'll have a hard time trying to find resources if you're doing it minecraft style. Search the surface for nodes of a resource you want, directly under that node is a vein you can mine in.

With that said, though, If you're insistent on doing it minecraft style, Probably no more than 15 blocks into the stone layer- Any deeper and you may miss veins that stop above your head.

Originally posted by A93ntZ3r0: I started mining for iron in a chunk near my base, by going deeper I discovered coal, nitrate, leed, sand, rocks, and of course clay in the same mine, not sure if this is the usual thing or I am very lucky.
https://steamcommunity.com/sharedfiles/filedetails/?id=2207842337

Edit:
Added a screenshot

Its usual. Any given vein has primarily whatever the rock was on the surface, and a little bit of two other major ores (Major ores being Iron, Lead, Coal, Nitrate) -- The sand you're finding is gravel, and of course clay from the dirt you dig past to get to the ore.