Best armor for Rangers: Gambeson of the Grand Empire

Gambeson of the Grand Empire is the best overall choice for Rangers—particularly those using firearms. It brings with it the following enchantments:
Steel-Threaded – Gives you +3 percent damage reduction.
Greater Gunnery – Your guns receive +15 percent reload speed.
Firearms in Avowed are single-shot weapons, meaning you’ll be doing a whole hell of a lot of reloading in between lining up those sweet headshots. Gambeson of the Grand Empire helps this along a bit with a much-appreciated 15 percent increase to your reload speed. It also offers decent protection, though your goal in battle as a Ranger should still remain not getting hit.
Where to find it

Complete the side-quest “Escape Plan” by helping Leoflaed and Glaedwine escape from the shanty town outside Paradis. There’s a whole bunch of stuff you need to find for them, and then after, choose to help them be smuggled out of town (don’t, whatever you do, report them if you want the armor!). Later in the game, you’ll find the pair safely living just in the entrance of Shatterscarp’s Thirdborn, to your left as you enter the town. They’ll give you the armor as a thank you.