Personally I like to use Blocking/Devastate/Random depending on the fight.
Reason for this is, I see no reason for using Revenge, as I'm not in need of threat.
I see no reason for using Last stand/Shield wall, as these shouldn't be necessary, unless something goes wrong.
Generally my third glyph depends on the fights. For example, I use Glyph of Sunder on Twins, as this will keep our fury warrior from having to apply sunders on the second twin.
On beasts its Glyph of Taunt, as taunt is really essential in this fight.
I think you see where I'm going with this :)
Personally I think the best bang for the buck glyph for running heroics is cleave.
I'd run with an all threat set consisting of cleave, devastate & block if I didn't min/max my glyphs for raiding.
I just found out you can swap glyphs as long as your are not in combat, in an instance... so with that said, glyph to your scenario... if your tanking multiple mobs glyph for AOE... Glyph of Resonating Power, Glyph of cleaving or HS, and glyph of sunder armor, or even glyph of shockwave... or even glyph of blocking if your taking to much damage.
If your at a boss... glyph for MT... Glyph of Taunt, Glyph of Blocking, Glyph of Devastate.
your going to have to experience what works best for you...