Science for auger blade, remember to remake the blade when you increase science.
Don't forget to upgrade SexRex until you get the auger. Longer mining/chopping.
I stayed with iron tools until 4 in both miner/rex, then swap to steel.
Higher level tools means more stuff per hit.
Once the durability drops below about half, go back, and combine it on a workbench to get back to max.
Shovel and sand/gravel is also good.
(even digging snow counts)
Stone axe though, counts as construction tools, so get a pickaxe/fireaxe asap.
stone shovel, mining tool.
Oh, I've had really really good luck, digging out clay pits. Generally below them is a ton
of iron etc (standard insane amount of rock), but depends on the map of course.
I do a LOT of digging, as those who've seen my streams can attest.
Going to have to see how the digger zombies affect things in A17 though.