It would depend on what you are "engaging"? If your talking people, the average adult male is about as hard to kill as a adult Mule deer. The vascular systems along with the amount of blood contained is very similar. I would think most any type of premium ammunition in the 165 to 180 gr. range would be a good place to start.
Heavy bullets excel in long range shooting scenarios better because of the velocity retention, along with their ability to be less susceptible to wind drift. Also, their time of flight to the target is quicker because of their ability to retain velocity, and not bleed it off as quickly as lighter projectiles do that start out faster, but shed velocity quicker. Hunting Shack Ammunition has recently introduced some excellent long range ammunition in various calibers, .30-06 being one of them. They are loaded with the excellent Berger VLD, (very low drag), bullets. I shoot their 210 grain VLD in my Kimber 8400 in .300 Win. Mag. with very good results. To date I sincerely doubt there is a better .30 cal. long range bullet out there.