It's not all that difficult to have every model in your army walk around with a 4++ or 3++ invulnerable save between Azrael, Jink, and Storm Shields. That is insanely efficient vs the more elite armies out there. However, this does limit your build options a bit. Since the codex makes it viable to give every model in your army a 4++ invulnerable, which greatly reduces the efficacy of opposing high ap weapons (like lascannons), it's probably not in your best interest to take ANY vehicles as they would give a fantastic target to those big weapons. This is totally fine, and you can make a strong, competitively viable list with no vehicles without too much difficulty, but I think it's important to highlight why it's in your best interest to stay away from them.

If being tough were all it took to be a top tier army, though, Iron Hands would still be terrorizing the scene (which they're not). You need to be able to bring the pain offensively as well. Dark Angels have one of the best Chaplains and Litanies in the game. Asmodai is a five wound Chaplain for 110 point who knows multiple litanies (unfortunately he can only use one though) and gives a +1 attack aura. +1 attack as an aura is a fantastic ability, and the new Dark Angel Litany allows you to move with your nearby infantry and count a stationary. This means you can move and shoot with bolter drill and not suffer penalties for moving and firing heavy weapons. With that, in addition to their durability, Dark Angels are starting to find their niche. They can exist at the strange intersection between Ultra Marines and Iron Hands with the ability to move and count as stationary while having incredibly durable units as well.

That's not all Dark Angels have, either. They have some especially unique units and rules that allow them to find their place competitively.

Let's start with my personal favorites: Sammael (Sammy) and Talon Masters. Sammy in a Land Speeder and 1-2 Talon Masters accompanying him has been a strong plug-and-play type of detachment for years, but they've gotten a lot of support recently to elevate them to a higher level. They can pump out a lot of firepower with a twin assault cannons and twin heavy bolters, rerolls to hit, reroll 1's to wound, and ignore cover, but they've suffered from a few unfortunate interactions. They are mobile, short-ranged units, which means they need to move into range of the enemy, but they have no mechanism to ignore the penalty for moving and shooting heavy weapons. They also have the old rerolls to hit (where you can't reroll the modified misses), which led to a whole bunch of lost efficiency. Now, though, Ravenwing has a Warlord trait to ignore the penalty for moving and firing heavy weapon within 6" of the model with that trait. That is absolutely fantastic for not only Sammy and his friends, but also random nearby attack bikes which make excellent screens for characters. They can zip to out of LoS positions quickly or pump out a larger amount of firepower while being tanky from a 4++ from jink. Ravenwing also got another Warlord trait to once per game count the active doctrine as a different one. This will allow you to stay in Devastator Doctrine for the first two turns of the game and actually make use of your mono-faction doctrine to engage the enemy without getting in harm's way with your Landspeeder/ Attack Bike entourage. Not only that, but you'll also be ap -2 for two turns as well!