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 by highlighting them with the deconstruction plans. This is limited by where you place Roboports, so using Long range power poles to place one down in the middle of the forest with a storage chest would work. Another option you can also use is 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. Your personal AOE for building and deconstruction can get significantly bigger than a regular roboport, and is always centered on you allowing you to take down entire forests a few minutes while barely moving. Note that you will need the inventory space for the wood if you use the personal roboports, and probably also a portable fusion reactor to power everything.