Guarding a Tank on TFB NiM can work for some groups. It depends a lot on your setups. For first phase, we normally guard the persons that take the most damage from lightning field and could be killed by heirad afterwards.
For the second phase and third phase, i think it's viable to guard a tank.
Definetly a good option indeed
Guarding dps should because of aggro problems should normally not be important. As an assassin i can generate about 50k threat in the first 10 seconds (don't know about other tanking classes). Even when melee dps is then pulling more then 5,5k dps in the first 10 seconds (range dps would even need 6,5k dps) you still have 2 taunts to easily get back on top of the aggro table.
Hmm ... 50k threat is tricky. Yesterday I did a TfB NiM on my slinger where I ripped of our vanguardtank in the 1st few seconds. I used my attackadrenal, serp assault proc and inspire. In 10 seconds time I generated 54k threat.
Thats with a guard and with a bugging surrender (which I will report as a bug in a seperate post).
@ the guy laughing at tanks who guard healers first:
How would you suggest determining which dps rips the most aggro? HP? no option, could be high endurence mods. High gear? he could be not very skilled.