The higher your rank with the gunsmith is, the better rewards you will receive. At rank 1 you get a package that may contain a legendary weapon. At rank 2 you will receive a class quest for a special legendary weapon; it's fairly easy and the weapon can only be used by one class. At rank 3 you will receive a call quest for an exotic primary, Hunter is Ace of Spades hand cannon, Titan is Fabian Strategy auto rifle, and Warlock is Tlaloc scout rifle. The other benefits is armsday orders. Each rank lets you pick up the same amount of orders and gives you the ranks amount of choices to pick from. (I.E. rank 1 one order, one choice. Rank 5 five orders, five choices for each order, etc) Having more choices will give you a better opportunity to get the weapon and perks that you want. If you decide that you don't like the weapons, you can place orders on all you classes and dismantle them for legendary marks.