I've heard a lot of people saying how annoying it is to not be able to farm anything as a Ranger. Of course, like any reasonbley intelligent person, I laugh at them. For farming Hill Giants as a Ranger is easy, once you exploit their AI(They are stupid...).
Equip in you skill bar the following skills(you may swap some in favor of your personal taste).
Troll Unguent
Storm Chaser
Pin Down
Flame trap
Barbed Trap
Incindiary Arrows(Found In Ring Of Fire)
Apply Poison(Optional)
Throw Dirt
First off, you can switch Incindiary arrows for Crippling shot and bring another preperation instead of pin down, if your a beginner. But any moderately skilled person will be able to do this. And if you want, switch Apply Poison for Distracting Shot, to intterupt the Giants Giant Stomp.
First, lay 2 Traps anywhere in the hill giant's area. Run up and aggro the first group(of 2) you see. Then Strafe or walk backwards to the traps. If they were clumped together, the plan worked. If they werent, then only one Giant is Crippled!
Just use Crippling Shot/Pin Down on the other giant to solve this temporarily. 
After they are both crippled, run backwards away form them until they drop aggro and start limping away(stupid, I know). Then Set 2 more traps and do the same thing. Also, choose one target to bring down first, then use incindiary arrows to cuase some massive damage on him, they are easy pickings as long as you keep them crippled with barbed trap. If for some reason you get gangbanged, consider taking the safer route and bring Crippling Shot, as opposed to Incindiary Arrows.
Tip: ALWAYS! Zone in once in the mission then die. Go back in a second time, THEN kill the hill giants, they never give more than a purple drop on the first run after the nurf. And only 1 Purple, if your very,very lucky. And even then, its no garuntee that you will be very successful. So try not to farm, the first time you enter the mission.
Happy Hunting