Before reading below, and for anyone who wants to correct my advice as a more experienced Death Knight, please note while this is not my first tank, I am new to Death Knights and still learning. I mainly tank 10+ keys, BG, and raid up to heroic (not so much heroic on this toon). Raiding and dungeons do have some different choices in Azerite traits, Essences, and 1 talent choice, but for the most part the traits don’t differ since like you’ll see mentioned below- they are all terrible…
Unfortunately, Death Knights have the worst Azerite traits, to the point where general traits are better than class traits. Their choice of Azerite pieces is mostly based on the minor traits such as Overwhelming Power.
There are some class traits which are ok, but you don’t want to get more than one.
Looking at your options, I would go with the following:
Take both Overwhelming Power traits (crucial trait), and Impassive Visage (also another solid trait).
Take Eternal Rune on your helm (this shines for raiding more than dungeons), as having 1 of that trait is always good.
For shoulders & chest, take 1 Bones of The damned, and 1 Bloody Runeblade. These two are also fine to have 1 of each. Bloody Runeblade does stack, but you don’t really need more than 1 unless you have no choice.
You could read up on the Azerite guides for Death Knights written on WoWHead and IcyVeins. The guide on WoWHead does a terrible job of ranking the traits, and pretty much keeps telling you to avoid all of them, but still has a good summary of each trait so you can read and decide on your own. I like the IcyVeins trait guide for Death Knights a bit more.
Things to keep in mind:
Marrowblood is your WORST trait.
Ring 2 and 3 traits are how you choose which Azerite piece is better (if you need to decide between 2 or more pieces of gear). The WoWHead Blood Death Knight guide’s Azerite trait section has a great breakdown of these and all Death Knight traits, and you can see a star next to the traits that are the best choices available.
Overwhelming Power, Impassive Visage, and Resounding Protection (the shield trait that’s basically Prydaz legendary from Legion) are you best choices in traits. Basically, Death Knight trait choices are based off of the best defensive traits you can take, not offensive.