I don't have a favourite because I've only hunted African plains game once. But my PH supplied his personal rifle for me to use, as he does with many of his clients. That rifle was also used extensively for culling on his property. It has killed several hundred head of game. The PH says this is ideal for him and his clients:
Sako AV deluxe 30-06 with Swarovski 3-9 x 40 scope, and a suppressor. Shooting handholds with Barnes TSX 168 gr. bullets at about 2850 fps. He uses it on everything up to Eland in size.
