For light engraving i like dental burrs, they hold up very well. I run they at speeds from 14000 to 60000 RPM.
I just flood the the area to be engraved with WD40 and let the tool create a puddle of Al mud!
BTW, The engraving quality and and how small you can get is only as good as the machine you have and Z axis positioning is very important.
RICH