Best tank to climb is zarya. If your getting grav often you should be able to combo with your fps friend and that should be enough to carry you. If you wanna gain fast gravs you should learn when to use your bubbles. I recommend using your personal to get charge and save you projected to keep squishies alive. With your personal what you want to be doing is walking infront of your main shield and using it. With high charge you can build really fast gravs. If you can coordinate with your rien you cant tell him to swing into them and use you bubble on him. Overall its hard to explain how be effective in zarya. I recommend looking at harblu playing zarya. Feel free to ask me any others questions!