You want to have a high damage output void weapon. Rocket launcher is good, heavy machine gun, etc. Honestly there are a couple of rare guns that are just as good as some legendary weapons but you want to do what you can to upgrade your weapons as soon as you can. Are you a member of a faction such as dead orbit, new monarchy, or future war cult? You typically get a weapon for ranking up with them and you can buy one when you reach rank 3.