World of Warcraft Warth of the lich king, the most popular lines for solo leveling tend to be Blood and Unholy. Every player tries to find the fastest way of WOW leveling as soon as possible. Unholy is more sustained DPS which specializes procs, pets, movement increases and Area of Effect damage. A lot of people prefer Unholy, because it tends to be the more "fun" oriented tree in the eyes of most. There are a few abilities that speed up your WotLK leveling:

Impurity is the main ability that amplifies the DKs spell damage. Like DK's already receive 25% parry rating from strength, this talent converts 25% of Attack Power into spell damage. This means your dots tick for more, and your deathcoils start hitting well into the thousands. This talent is almost mandatory for any DK thinking of going unholy.

Ebon Plaguebringer combined with the above talent are what make Unholy a sustained DPS. These abilities amplify your dots and magic damage even further. Not only does this affect your commonly used frost fever and blood plague, but other talents if you so choose; Wandering Plague or Unholy Blight benefit as well as other AoE skills like Pestilence and Bloodboil.

Master of Ghouls, this talent allows the ghoul you summon to be controlled by you, and become permanent. Your ghoul with the Ravenous Dead talent, gains 60% of your personal strength and stamina, and you can also choose to get a glyph which gives your ghoul another 20% of your strength. These combined allow your ghoul to do some serious damage. Being able to control your ghoul; like the hunter pet, gives you the option to "leap", "stun", "claw" and "huddle".

Some players will find the unholy tree is very hard to skip over talents. And almost every talent in it is useful and hard to turn up. It may not be the greatest 1v1 spec over a short duration fight, but for long boss fights or AoE, you will find Unholy to be a strong talent tree choice. Blood and Unholy are both very useful, when deciding between Blood and Unholy, personal preference and play style should be the deciding factor. For me, at present, I leveled to 75 with blood then switched to unholy until 80, but could of gone either way. Frost is not a bad tree, just not a popular one for WotLK Power leveling.

Click here to check on WotLK Leveling Blood article.