For the first trip, the one that you shoot the best.
Most of us don't go to Africa every year, so when we go it is something special. A strange place, animals that you've never hunted before, a PH at your side and trackers watching over your shoulder. It all adds up to a new unsettling experience, having "old Faithful" in your hands makes that first shot a lot easier.

The second time you'll use a 375 H&H because it's what old time Africa hunters like you always use.

The third time you will use a big double rifle because that's what the PH's use.

The fourth time you'll take the rifle that you shoot the best.

For me it was:

#1 30-06 and 375 H&H ( I was hunting Buffalo in addition to plains game) in M-70's.

#2 375 H&H - Krieghof double

#3 next year - I'm not sure maybe a 7X57