Well in my opinion its better on a matriarchal bow, because you get a lot more equipment flexibility which will benefit you a lot, however im aware most ppl think that gmb is better. So i suppose its just a matter of what are you going to wear.
the problem with GMB/Matri is that it's amazon only...
I mean, if i had the funds to make such a runeword, due to its high price, i would make it in a non-class-specific item so i could use it on my hunters/rangers/whatever as well.
(I'd personally make it out of a diamond bow, since i love high min dmg, but then it would get almost worthless to most ppl, so it wouldn't be tradeable)