Well going that route I may change things a little although it will still be one mans opinion.
1. 22 Rimfire
2.38 Special/357 Mag
3. 9MM Para.
4. 222 Rem.
5. 45-70 Gov.
6. 7x57 Mauser
7. 303 British.
8. 30-30 Win
9. 30-06 Springfield
10. 300 H&H
11. 375 H&H
12. 44 Special/44 Mag.

This list of cartridges has enjoyed long life and in many cases started or changed a trend. It's about impossible to leave the 270 off the list and of course, I never would.. Same for the 6.5x55.