Well the 20 agility would give 40 AP which is slightly less than the 44 AP of crusher. So just based on AP Crusher is slightly better. However Agility gives a small amount of crit (nice for hunters) and a small amount of dodge (meh).
Not a 100% sure but wouldn't they be roughly equivelent?
Are you guy considering spec yet? BM gets a 25% boost to AP while Survival gets a 10% increase in agility
BM
20agix2=40AP+25% = 50AP
44AP+25% = 55 AP
Sur
20agi+10%=22agix2 = 44AP
44AP = 44AP