I listened to both albums last night. I still can't decide. Both have their good points and their "meh" points.
I will say this, if I only listened to side 1 of Angel Witch, I could easily vote for Diamond Head. That first side of AW is extremely yawn-worthy. It isn't bad, but it's nothing special. Side 2 really grabs me though and based on that alone, they could almost garner my vote.