Ok, TODAY I'd choose:
1) 1911 with top ends or barrels for .22, 9mm, .38 Super, 9x23, .40, .357 Sig, .400 Corbon, 10mm, .45 acp and .460 Rowland.
2) GLOCK 35 with top ends or barrels to create a: 17, 22, 31, 34, 37 and a .22 conversion.
3) Smith and Wesson Model 29 w/ 6" barrel.
3 guns, 13 different calibers.