Here are some suggested specs to help guide you leveling as a Death Knight. Focusing on the Death Knight’s Blood tree when leveling will help you minimize downtime through all of your self-healing abilities, along with still providing a high level of damage.
WotLK Death Knight - Ebon Hold
Death Knight Leveling Spec (Blood)
Two of the must-have abilities in this spec are Butchery and Vendetta. They return a huge amount of runic power and health every time you kill a mob that grants experience. It would be wise to include at least those two abilities in any Death Knight Leveling build.
Mark of Blood is also available early on, which should all but remove your need to ever need to eat or bandage while leveling. This provides a huge advantage to other classes and even other Death Knight specs. While not available until much later in the tree, Bloodworms and Vampiric Blood help improve your leveling time significantly. If you find you aren’t ever losing enough health to need Rune Tap, you can drop it for higher damage abilities in either the Blood or Unholy trees.
Blood (65 points) 2/2 Butchery 3/3 Subversion 5/5 Blade Barrier 5/5 Bladed Armor 3/3 Scent of Blood 2/2 Two-Handed Weapon Specialization 1/1 Rune Tap 5/5 Dark Conviction 3/3 Death Rune Mastery 3/3 Improved Rune Tap 3/3 Vendetta 3/3 Bloody Strikes 3/3 Veteran of the Third War 1/1 Mark of Blood 3/3 Bloody Vengeance 3/3 Bloodworms 2/2 Blood Aura 5/5 Sudden Doom 1/1 Vampiric Blood 3/3 Might of Mograine 5/5 Blood Gorged 1/1 Dancing Rune Weapon Frost (0 points) None Unholy (6 points) 2/2 Vicious Strikes 3/3 Morbidity 1/2 Epidemic
Death Knight Leveling Spec (Unholy)
Again, this spec relies on Vendetta and Butchery for the health and runic power restoration while leveling. Instead of being as oriented toward melee damage, however, the Unholy spec focuses on Ghouls, magical damage, and Area-of-Effect abilities (primarily Corpse Explosion).
Good variation of this build are possible by going deeper into the Blood tree, possibly including Rune Tap and Bladed Armor, depending on your play style and downtime between pulls. Alternatively, dropping Two-Handed Weapon Specialization and Dark Conviction would allow you to get some of the more powerful talents deep in the Unholy tree.
Blood (19 points) 2/2 Butchery 3/3 Subversion 5/5 Blade Barrier 3/3 Scent of Blood 3/3 Death Rune Mastery 3/3 Vendetta Frost (0 points) None Unholy (45 points) 2/2 Vicious Strikes 3/3 Morbidity 2/2 Epidemic 3/3 Ravenous Dead 3/3 Outbreak 5/5 Necrosis 1/1 Corpse Explosion 3/3 Blood-Caked Blade 1/1 Shadow of Death 1/1 Summon Gargoyle 5/5 Impurity 3/3 Reaping 1/1 Master of Ghouls 5/5 Desecration 3/3 Crypt Fever 3/3 Ebon Plaguebringer 1/1 Scourge Strike
Conclusion
Choosing a spec is largely comes down to personal preference and play-style. However, some abilities such as Butchery and Vendetta are going to greatly improve the speed you can level no matter which tree and abilities you prefer. Even if you are not a fan of the melee oriented Blood tree, if you plan on leveling solo, you should consider it a very strong option if you plan on leveling as quickly and easily as possible.
