Just my $0.02, but I prefer ACME over OJ just becasue the ACME will bend. If you do hit something of any real size the ACME, being made of brass, it will bend and take the damage where as the OJ, since it's made of stainless steel might transfer more shock and damage to other potential weak points in the drivetrain. Would you rather replace a $400-500 prop, or spend several thousand to replace prop, prop shaft, v-drive, etc.? That's just my take on it.
I had some damage to my prop last season while hitting a stick when backing off the trailer. It only bent the tip of one blade, but it made a lot of vibration. I took a pair of channel locks and bent most of the damage out and rode the rest of the day. I couldn't have done that with an OJ I bet.