The first question is if you want the "Chief, Smash!" achievement. If yes, then take the Gravity Hammer. Next, to make the Knights easy, take the Incinerator Cannon. Use it (possibly doing a quick switch with a Lightrifle if you find one from a downed Knight) to get through the room, using the Lightrifle/Grav Hammer on the Crawlers and the Cannon on the Knight's and Watchers. That's how I got through the part and achievement on Legendary.
If you don't care for the achievement, ignore the hammer, just take the Cannon and Lightrifle.