I used a standard BM dps spec to solo most of the level-80 heroics. I don't think any spec but BM would have had as easy a time on Devourer of Souls at the end of H-FoS due to the self-healing requirements.
If you use a Spirit Beast as BM, your self-healing capability through Spirit Mend is greater than what Chimera Shot on cooldown gives you as MM, and without any armor or health talents, Mend Pet is still just sufficient to outheal the incoming damage of most ICC5 heroic bosses on a ferocity pet.
So...
SV: Best damage output, best CC, best healing via 2pcT5
MM: Best self healing not reliant on a specific (non-tenacity) pet, only spec with an interrupt, 2nd best 2pcT5 healing
BM: Spirit Bond, Spirit Mend (w/Spirit Beast), best pet threat without using GCD's on MD, best tenacity pet tanking w/out 2pcT5 (but also the worst potential benefit from that set bonus)
They all have their perks. Too bad we can't tri-spec.
[Edit: Oh, another unique Spirit Beast perk (go go Loque'nahak)! I had trouble on Leotheras because apparently he doesn't consider a pet a valid target for his Chaos Blasts. So I feigned death out of LoS behind the wall about 60 yards away and let Loque solo him. Completely. Spirit Mend (used manually, on CD -- the pet AI will only autofire it at 50% HP, which is too late) was sufficient to keep the pet topped off without any need for Mend Pet. When Leo was finally getting low (yeah, it took a while), I jumped back up, popped all CD's, and machine gunned his face off. Of course the gloves didn't drop.]