Cobalt Chainsaw

The mechanical tools swing faster than the Cobalt Waraxe but cut a shorter distance from where you stand, so you have to get close to the trunk. If you have not stacked speed bonuses yet, the raw speed wins and the chainsaw is the better pick. Once you are running a proper mining loadout with the speed accessories and armor, the axe pulls back ahead.

The feel is different too. It fires a continuous beam rather than a swing, which is easy to hold steady on a tree but awkward in a tight tunnel where the reduced reach costs you a tile you needed. It and the waraxe are alternatives, not a pair, so keep whichever suits your loadout and sell the other.