I own, or have owned, an M1903A1, an M1 Garand, an M1A, an AR15Match, a #1MkIII(2A), several SKS's, a K98, an 1898Mauser, an 1896Mauser, an M39 (Finn Mosin), an SVT40, and a 'poor man's M40' (Savage 10FP).
The only ones I received combat training with are the M1 and the M14. The only one I ever carried in combat is the M14.
I vote for the M14, because I know it's capabilities from experience.
I find the accuracy and terminal performance of the AR disappointing.
If I was in an urban theater, I would go for the AK74. If it was chambered in 5.56, so much the better.
With my 10FP .308 that shoots well under 1/2MOA with 180gr Sierras handloads, I would not hesitate to go for Osama. (Actually, it occasionally shoots better than 1/4MOA, but if I said that in certain locales, I'd get called a liar)(Talking to BR folks about factory rifle accuracy can often be an exercise in frustration, don't you think...?).
Greg