Hard to argue with that lineup. A .22LR semi‑auto is pure utility and fun, and 5.56 covers a ton of ground. That .45‑70 mention is great too.An impossible question to answer by any gun crank, particularly if specific purpose driven.
But for me, that's be the .22LR rimfire in a semi-auto rifle.
If it had to be a centerfire cartrige it'd be the 5.56/.223 in a semi-auto rifle.
Notable mention if I could add a .45-70 single shot to either of the above.