Unholy Death Knight has one of the highest AOE potential, with a nice single target damage and [Ebon Plaguebringuer] to buff the raid, this increases the damage of magical spells by 13% and disease damage.

Rotation for Unholy Death Knight Wotlk

Unholy Death Knight Rotation and Priorities

Diseases (Icy Touch/Plague Strike) > Blood Strike (Blood Runes) > Scourge Strike (Frost Runes + Unholy Runes) > Death Coil to dump runic power > refresh diseases with pestilence > pop CDs at the right moment

Tips

Never allow diseases to drop, most of the damage from abilities drop without diseases.

Get to know the fights to pop cooldowns at the best times (low movement, no crowd control, AOE, etc).

Time cooldowns so they can be used to clean thrash and be ready at boss fights.

Use anything that amplifies stats before using [Summon Gargoyle] has the increase of the stats won’t apply if it was already summoned.

Know the presences, frost can help if there is a lot of incoming damage, unholy boosts the DPS on high mobility bosses (ex. Professor Putricide), and Blood presence gives the highest DPS in low movement fights. Timed well unholy presence can be used to close gaps and swaping back to blood presence in the right moment can increase the overall DPS, however knowledge of the boss fight is needed to not incur in a DPS loss, has runes will have to be sacrificed to swap presences.