Deathguard - New

The Death Guard are one of the Traitor Legions of Chaos Space Marines. They worship and devote themselves exclusively to the Chaos God Nurgle and as a result of his mutational "gifts" they have become Plague Marines; Astartes who are eternally rotting away within their power armour and infected with every known form of disease and decay but who are immune to all pain or minor injury. Their bodies are hives of filth and decay, their flesh eternally rotting away even as it is renewed by the ceaseless process of death and rebirth. The Death Guard are entirely steeped in the power of Nurgle, the god of death and plagues, their very essence the epitome of all that vile Chaos God stands for.

Death Guard have lots of great mid-range shooting and the ability to maintain double shots on rapid fire bolt weapons while on the move, but lack some heavy weapons and long-range firepower. Death Guard are extremely resilient. The main idea is to soak up dozens of wounds with troops' disgustingly resilient rolls while protecting your characters for their aura abilities. Death Guard is an army that can be very beginner-friendly

The newest Death Guard Combat Patrol box would probably be the best way to start building a modern Death Guard army. Alternatively you can pick up a box or two of Plague Marines.

Mortarion, Typhus, Nauseous Rotbone Plague Surgeon

If you are seeking a competitive army, then the answer depends on the meta at the time, as every army has its ups and downs in the competitive community. Casual players should not worry about good/bad as it's all about fun.

Usually dark green armor with browns to show dirt & decay, along with purples and reds for diseased fleshy parts typical of the Nurgle.