Depended on what target animal I as after. I shot a 25-06 at smaller plains game and baboons. Then 30-06 for zebra, kudu and Gemsbuck. then .375H&H and .416 Rigby for the ones in the Big 5.
For those of you that dream of Africa but doubt you will get there. I hope you are able to get it figured out and make the trip happen. It is not as expensive as you think, and you can cut the cost in half by only bringing pictures back. Much of the cost is sending stuff back stateside. Also, renting guns is an easy button. You can also go on a cull hunt if you don't plan to bring anything back and they are really cheap, but still the same experience. Go as soon as you can, as you will want to have those memories for the rest of your life, and the sooner you go, the longer you will have them.