Since I'm not sleeping I thought I would compile what everyone has said so far on the thread. Some of this stuff is interpolated because some chose 5 or 6 calibers. .243 was added to those who only chose 2.
Shotguns are not included below- eventhough they are extremely versatile.

.204 1
22lr 18
22 Mag 4
.223 7
.22-250 3
.243 33
6mm 1
.25-06 5
.270 9
7mm-08 3
.280 1
7mm Rem Mag 16
30/30 1
.308 7
30-06 15
300wsm 3
300 Rsaum 1
300wm 10
300 Ultra Mag 2
.338-06(Federal)2
.338 Win Mag 16
.340 Wby 1
.338 RUM 1
.338 Lapua 1
35 Whelen 1
9.3X62 1
.375 Ruger 1
.375 Ruger 1
.376 Steyr 1

The jury seems to feel that the best of the best is the .243. with a second place going to the 22LR. Third place is a tie going to 7mm Rem Mag and.338 Win Mag, with the venerable 30-06 coming in next. The 300 WM also shows great support.

Have a great day.