All three specs are very capable of tanking anything that is put infront of you..Unholy and Frost used to be THE tanking specs.
Frost is generally a better choice for players at lower gear levels. This is solely because of the types of tools that it provides are not as dependant on high stats and gear requirements as some of those Unholy offers. Frost also provides the snap threat that Unholy cannot in the form of Howling Blast, Threat being a key problem to many lower geared tanks.
The reason many people choose Blood these days is because in essence, Effective Health reigns supreme and the other specs simply cannot offer what Blood does in this area.
Unholy's Key talent, Bone Shield really starts to take effect once higher gear levels come in, Higher avoidance means a higher chance of Bone Shield lasting its full duration, As far as your point on the "SUPER BUFF!", Unholy is designed for caster utility, Whereas Frost caters to Melee Utility.. Icy Veins vs Ebon Plague
- Frost = Entry level tanking and "user friendly"
- Frost = Melee Utility
- Unholy = Picks up as a tanking spec with slightly more progressed gear setups.
- Unholy = Caster Utility
- Blood = Larger Effective Health pool, Great for geared out tanks
- Blood = Progression Tanking