As far as i know, this has been a big point in halo wars multiplayer.
If you have played halo wars for a long time, you will know that-
a)Scorpions special (y) ability is stronger than grizzlys but grizzlys ability is more spread out, and is more effective against infantry.
b)Grizzly can overall gain more stars (14), scorpion can gain only 13.
c)Scorpions are easer to make at start of the game and they are cheaper to upgrade(400+900=1300)
(half the cost if you are anders), to get grizzly, you have to spend 400+900+1800=3100
So yeah, how do you think?