Here's a take:

1) Sharps 45-70 Carbine / Henry repeater (tie)
2) Colt SA
3) Winchester 1895 .405
4) Browning M-2 .50 BMG
5) Browning M-1911 / Hi-Power (tie)
6) A.H. Fox SxS 12 ga. FE grade
7) Parker A-1 Special 28 ga.
8) Thompson M-1
9) M-1 Garand (actually Canadian design, but commissioned by US military)
10) M-1 A
11)Remington 870
12)Stoner AR-15

Best guns ever: MAUSER 98 / AK-47 (tie)

Americans???