It is mostly a matter of opinion. As mentioned previously, I beat the DG with Fishron Wings and Vampire Knives. (Not for healing of course! But because Vampire Knives fire a bunch of projectiles at once - the more projectiles, the more +1 damage potential. And I didn't need to worry too much about accuracy.) In my opinion, that's easier than gathering huge piles of silt or exploring worlds hoping for a chest to contain the right item.
It probably comes down to definition of easiest. The Bone Key is 'easy' to obtain in that you know exactly how to get it. Amber Mosquito is luck and might require thousands upon thousands of silt/slush/fossil. Lihzahrd Egg is also luck-based and might require thousands of lizard kills. (It took me six hours if memory serves correctly.) And so on...
Anyway, that's all from me - I'm going a bit off-topic.