I'm not a savant of Axton by any means but from what I've experienced using him first hand in groups(Never solo'd yet) his slag turret is an incredible tool. Maximize on his damage and grenade boost skills to reach incredible damage off explosive weapons(grenade damage boost splash damage which all torgue guns deal) such as the harold will provide incredible damage dealing potential.
I tend to run this build: http://www.bl2skills.com/commando.html#25055153015105515010015000000000
With these tools:
-Harold(easy to get in torgue dlc) -Bonus package(torgue dlc again) -Swordsplosion(Tiny dlc quest reward) -slag weapon of choice in case turrets are down, I stick to the slag avenger but that might not --be available to you.(I tend to throw a bunch of these and a bonus package or two to really hurt the baddies) -moxxie creamer for health gating(gotten from that wildlife preserve arena)
Shield and class mod is up to your comfort.
Relic is explosive damage
--- Lv61 Zero build: http://www.bl2skills.com/assassin.html#000000000055053105015505515401
As said before, spec Axton to be an explosive expert. Then farm for an incendiary Gunerang and Babymaker, as well as a good slag grenade and a relic that increases fire damage. Using these tools, you can take down Hyperius and Voracidious in less than a minute if everything goes right during the fight. Check out these videos for example.
http://youtube.com/watch?v=beLHLVcnd9s --- Dib: Sorry, I'm late. Horrible nightmare visions! Ms. Bitters: It's called life, Dib. Sit down.
You can also get the Norfleet from Vermivorous, who, while having stupid high hp, can be easier to deal with than Hyperius for some; especially if it runs into a train. But of course Verm can be a pain to spawn.
What's the easiest way to get to Bunker/farm him?
Well the only way to the BNK-3R is through Thousand Cuts, and from there, you just gotta grind out fighting it until it drops the Sham, and then hope it's the one you want, no real special ways to make that go any faster.