Early on, Flamethrowers, Shotguns, and Poison capsulse are the best as noted by other answers.

Later on in the game, you can have drones Harvest them for you. This is limited by where you place Roboports, but you can also use Modular armor and the Personal roboports to do so on the go. a personal roboport allows for 10 bots in a moderate area around you to construct and deconstruct things, with 2 charge ports for them before they go back into your inventory. Adding additional ports to the armor increases the range, the number of bots by 10, and adds 2 more recharging ports. Note that you will need the inventory space for the wood.