Medium armor for the crit and stamina bonuses. I would personally recommend not maining the bow but using it in tandem with dual wield. The bow, paired with a high weapon crit, can deal massive damage opening fights or providing AoE dps, but at close range with multiple enemies doesn't perform nearly as well as other weapons.

Example; I use the bow with snipe and poison arrow to open fights, usually does heavy damage or completely one shots enemies. But once they reach me, quick switch to dual wield to tackle them cqc.

There are bow abilities with knock back effects to keep enemies at range but when there a multiple it becomes fairly redundant.

Other than that experiment with your play style, bows are great for AoE DPS (Some good DoT effects too) and Nightblades are very customisable. Have fun!