For me I would go with my Mod. 94 Winchester 30-30. It is light weight, compact, fast action, and has enough power for hunting and defense. It would really suck to be limited to one caliber, but the 30-30 would do what I need in any situation.
I would have loved to build an M4 platform .243, but after running the details, the .223 wins.
If I had unlimited quantity to last a lifetime, I would take .50BMG thank you very much.. I think it is fairly effective on almost all living creatures in this part of the Solar System and I would probably get pretty skilled using it, if ammo was unlimited
Yep, no such thing as overkill.